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LPI Contribution No. 1331

WORKSHOP PROGRAMAND ABSTRACTS

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NASA Mars Data Analysis Program

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Jim Papike University of New Mexico

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Brad Jolliff Washington University in St. Louis

Virgil Lueth New Mexico Institute of Mining and Technology

Douglas Ming NASA Johnson Space Center

John Mustard Brown University

Clive Neal University of Notre Dame

Chip Shearer University of New Mexico

Allan Treiman Lunar and Planetary Institute

Dave Vaniman Los Alamos National laboratory

Lunar and Planetary Institute 3600 Bay Area Boulevard Houston TX 77058-1113

LPI Contribution No. 1331

Compiled in 2006 by LUNAR AND PLANETARY INSTITUTE

The Institute is operated by the Universities Space Research Association under Agreement No. NCC5-679 issued through the Solar System Exploration Division of the National Aeronautics and Space Administration. Any opinions, findings, and conclusions or recommendations expressed in this volume are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration. Material in this volume may be copied without restraint for library, abstract service, education, or personal research purposes; however, republication of any paper or portion thereof requires the written permission of the authors as well as the appropriate acknowledgment of this publication.

Abstracts in this volume may be cited as Author A. B. (2006) Title of abstract. In Workshop on Martian Sulfates as Recorders of Atmospheric-Fluid-Rock Interactions, p. XX. LPI Contribution No. 1331, Lunar and Planetary Institute, Houston.

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ISSN No. 0161-5297

PPPRRREEEFFFAAACCCEEE This volume contains abstracts that have been accepted for presentation at the Workshop on Martian Sulfates as Recorders of Atmospheric-Fluid-Rock Interactions, October 22–24, 2006, Moffett Field, California. Administration and publications support for this meeting were provided by the staff of the Publications and Program Services Department at the Lunar and Planetary Institute.

Workshop on Martian Sulfates as Recorders of Atmospheric-Fluid-Rock Interactions v

CCCOOONNNTTTEEENNNTTTSSS

Program .........................................................................................................................................................................1 Terrestrial Sulfates in an Extreme Acid Mine Drainage Environment: The Richmond Mine at Iron Mountain, California

C. N. Alpers ...............................................................................................................................................7064

The Sedimentary Rocks Exposed in Terra Meridiani R. E. Arvidson............................................................................................................................................7043

Detection of the Hydration Phase of Martian Sulfates Using Emission Spectroscopy of Magnesium and Calcium Sulfates

A. M. Baldridge and P. R. Christensen .....................................................................................................7041

Tranformation of Jarosite to Hematite in Simulated Martian Brines V. Barrón, J. Torrent, and J. P. Greenwood .............................................................................................7052

Differentiantial Mobility of Uranium and Thorium in Aqueous Solutions as Potential Indicator of Past Geochemical Environment on Mars

A. T. Basilevsky, B. N. Ryzhenko, and A. M. Abdrakhimov .......................................................................7031

Mineralogic Diversity of Mars and Discovery of Sulfate Deposits from the OMEGA/Mars Express Investigation

J.-P. Bibring and OMEGA Team .............................................................................................................7073

Sulfate Mineral Analysis by the CheMin XRD/XRF Instrument on MSL D. L. Bish, P. Sarrazin, D. Blake, D. Vaniman, and S. Chipera................................................................7018

VNIR Spectra of Sulfates Formed in Solfataric and Aqueous Acid Sulfate Environments and Applications to Mars

J. L. Bishop, A. J. Brown, M. Parente, M. D. Lane, M. D. Dyar, P. Schiffman, E. Murad, and E. Cloutis...........................................................................................................................7037

The Mars Science Laboratory (MSL) Mission D. L. Blaney...............................................................................................................................................7034

Martian Sulfate Mineralogy from Spectroscopy: Ground-based, Orbital, and In Situ Perspectives D. L. Blaney, D. Glenar, W. Maguire, and G. Bjoraker............................................................................7035

Extremophile Microorganism Transformations of Sulfates and Other Sulfur Minerals in Surface and Subsurface Environments

P. J. Boston, M. N. Spilde, and D. E. Northup ..........................................................................................7070

Use of the Thermal and Evolved-Gas Analyzer (TEGA) on the Phoenix Lander to Detect Sulfates on Mars

W. V. Boynton and D. W. Ming .................................................................................................................7065

Remote Sensing of Western Australian Sulfate Deposits and Applications for Mars A. J. Brown ................................................................................................................................................7063

Sulfur on the Martian Surface: In-Situ Data from All Landing Sites J. Brückner and APXS Team ....................................................................................................................7002

vi LPI Contribution No. 1331

Atmospheric Conditions on Early Mars and the Missing Layered Carbonates M. A. Bullock and J. M. Moore .................................................................................................................7068

The Role of Fluid Chemistry and Crystallization Kinetics in Na and K Zoning in Jarosite P. V. Burger, J. J. Papike, C. K. Shearer, and J. M. Karner.....................................................................7019

Intrinsic Acidity of Jarosite and Other Ferric Sulfates as an Indicator of How They Form D. M. Burt .................................................................................................................................................7005

Impact Excavation of Sulfides That Then Weather into Sulfates: An Astrobiology-Friendly Explanation for Acid Sulfate Formation on Mars

D. M. Burt, L. P. Knauth, and K. H. Wohletz ............................................................................................7004

Mapping Sulfates in Nevada Using Reflected, Emitted, Multi-Spectral and Hyperspectral Systems W. M. Calvin, R. G. Vaughan, C. Kratt, and J. D. Shoffner ......................................................................7029

Cracks and Fins as Evidence for Water Evaporation and Condensation Associated with Temperature Changes in Hydrous Sulfate Sands

G. V. Chavdarian and D. Y. Sumner .........................................................................................................7008

Water Content and Dehydration Behavior of Mg-Sulfate Hydrates S. J. Chipera, D. T. Vaniman, and J. W. Carey .........................................................................................7026

Direct Chemical Analysis on the Martian Surface: A Review of Sulfur Occurrence and Interpretation from Viking to MER

B. C. Clark.................................................................................................................................................7010

Laser Induced Breakdown Spectroscopy (LIBS) Remote Detection of Sulfates on Mars Science Laboratory Rover

S. M. Clegg, R. C. Wiens, M. D. Dyar, D. T. Vaniman, J. R. Thompson, E. C. Sklute, J. E. Barefield, and S. Maurice.............................................................................................7059

Estimating Minimum Volumes of Water Involved in Formation of Sulfate Evaporite Deposits M. Coleman and D. Blaney .......................................................................................................................7047

Stable Isotope Characterization of Microbially Produced Sulfate: Field Data Validation at Río Tinto of New Laboratory Culture Experiments

M. L. Coleman, S. Black, B. Brunner, C. G. Hubbard, T. J. McGenity, R. E. Mielke, and J.-Y. Yu..........................................................................................................................7036

Sulfate Stability Under Simulated Martian Conditions M. Craig and E. A. Cloutis ........................................................................................................................7013

Mixing and Re-Solution Processes Affecting Evaporite Mineral Distributions on Earth and Mars J. K. Crowley, J. S. Kargel, G. M. Marion, S. J. Hook, N. T. Bridges, A. J. Brown, and C. R. de Souza Filho ......................................................................................................7056

Sulfate Brine Stability Under a Simulated Martian Atmosphere J. Denson, V. Chevrier, and D. W. G. Sears..............................................................................................7066

Mössbauer Spectroscopy of Synthetic Alunite Group Minerals M. D. Dyar, L. Podratz, E. C. Sklute, C. Rusu, Y. Rothstein, N. Tosca, J. L. Bishop, and M. D. Lane.....................................................................................................................7053

Lifetime of Jarosite on Mars: Preliminary Estimates M. E. Elwood Madden and J. D. Rimstidt .................................................................................................7007

Workshop on Martian Sulfates as Recorders of Atmospheric-Fluid-Rock Interactions vii

Sulfate Formation and Its Relevence to Environmental Conditions on Early Mars C. Fan, D. Schulze-Makuch, and H. Xie....................................................................................................7033

Raman Imaging Analysis of Jarosite in MIL 03346 M. Fries, D. Rost, E. Vicenzi, and A. Steele ..............................................................................................7060

Martian and St. Lucian Jarosite: What We Can Learn About Meridiani from an Earth Analogue J. P. Greenwood, M. S. Gilmore, A. M. Martini, R. E. Blake, M. D. Dyar, J. A. Gilmore, and J. Varekamp ................................................................................................................7050

Cathodoluminescence Study of Phosphates in the Y000593 Nakhlite A. Gucsik, H. Nishido, K. Ninagawa, T. Okumura, N. Matsuda, M. Kayama, J. Götze, J. Z. Wilcox, Sz. Bérczi, Á. Kereszturi, and H. Hargitai.............................................................7049

Trace Elements in MIL 03346 Jarosite: A Record of Martian Surface Processes? C. D. K. Herd ............................................................................................................................................7012

Experimental Preservation of Amino Acids in Evaporitic Sulfate Minerals as Analogs for Surficial Processes on Mars

A. Johnson and L. M. Pratt .......................................................................................................................7061

Sulfur Solubility in Martian Mantle Melts: Impacts on the Late Noachian Atmosphere S. S. Johnson, M. T. Zuber, T. L. Grove, and M. A. Mischna ....................................................................7038

Review of Recent Theoretical Models of Salt Sequences and Solution Compositions on Mars P. L. King ..................................................................................................................................................7044

Sulfates and Other Salts on the Martian Surface Have Their Source Deep in the Crust G. G. Kochemasov.....................................................................................................................................7016

Dissolved Sulfate Analysis on the 2007 Phoenix Mars Scout Mission S. P. Kounaves, S. M. M. Young, J. A. M. Kapit, and hoenix Team .........................................................7020

Active and Noble Gas in Terrestrial Jarosite- and Alunite-hosted Fluid Inclusions: Insights and Constraints on Formation of Martian Sulfates

G. P. Landis and R. O. Rye .......................................................................................................................7027

Determining the Chemistry of the Bright Paso Robles Soils on Mars Using Multispectral Data Sets M. D. Lane, J. L. Bishop, M. Parente, M. D. Dyar, P. L. King, and E. Cloutis ........................................7025

Radiolytic Oxidation of Pyrite: A Viable Mechanism for Sulfate Production on Mars? L. Lefticariu, L. M. Pratt, J. A. LaVerne, and E. M. Ripley.......................................................................7048

Sulfates as Geochronometers/Geodosimeters for In-Situ Mars Surface Science K. Lepper, T. Morken, and A. Podoll ........................................................................................................7054

Textural and Stable Isotope Discrimination of Hypogene and Supergene Jarosite and Environment of Formation Effects on 40Ar/3 9Ar Geochronology

V. W. Lueth ................................................................................................................................................7028

Evolved Gas Analysis on the 2009 Mars Science Laboratory P. R. Mahaffy and H. B. Franz ..................................................................................................................7014

Sulfate Deposits and Geology of West Candor Chasma, A Case Study N. Mangold, A. Gendrin, C. Quantin, B. Gondet, and J.-P. Bibring .........................................................7039

viii LPI Contribution No. 1331

Sulfate Geochemistry and the Sedimentary Rock Record of Mars S. M. McLennan, J. P. Grotzinger, J. A. Hurowitz, and N. J. Tosca .........................................................7045

Extra-Martian Origins of C, Fe, Ni, S and Cl Elements to Form Deposits as Local Cycle System on Mars

Y. Miura.....................................................................................................................................................7001

Mars-Analog Brines and Evaporite Experiments: Implications for Sulfates J. M. Moore and M. A. Bullock .................................................................................................................7032

Iron Sulfates at Gusev Crater and Meridiani Planum, Mars R. V. Morris and Athena Science Team....................................................................................................7042

Looking Forward to CRISM S. Murchie, R. Arvidson, P. Bedini, J.-P. Bibring, J. Bishop, P. Cavender, T. Choo, R. T. Clancy, D. Des Marais, R. Espiritu, R. Green, E. Guinness, J. Hayes, C. Hash, K. Heffernan, D. Humm, J. Hutcheson, N. Izenberg, E. Malaret, T. Martin, J. A. McGovern, P. McGuire, R. Morris, J. Mustard, S. Pelkey, M. Robinson, T. Roush, F. Seelos, S. Slavney, M. Smith, W.-J. Shyong, K. Strohbehn, H. Taylor, M. Wirzburger, and M. Wolff...................................................................................................7022

Multi-Instrument Sulfate Detection and Mineral Stability on Mars J. F. Mustard .............................................................................................................................................7055

The Challenge of Returning Hydrated Sulfates from the Surface of Mars to Earth C. R. Neal ..................................................................................................................................................7058

Correlations Bewteen Sulfate and Hematite Deposits as Observed by OMEGA E. Z. Noe Dobrea.......................................................................................................................................7071

Terrestrial Analogs of Martian Sulfates: Major and Minor Element Systematics of Selected Jarosite Samples

J. J. Papike, P. V. Burger, J. M. Karner, C. K. Shearer, and V. W. Lueth ................................................7009

Jarosite-Alunite Crystal Chemistry J. J. Papike, J. M. Karner, and C. K. Shearer ...........................................................................................7003

Crystal Molds on Mars: Melting of a Possible New Mineral Species to Create Martian Chaotic Terrain

R. C. Peterson............................................................................................................................................7015

Geology of Sulfate Deposits in Valles Marineris C. Quantin, A. Gendrin, N. Mangold, J. P. Bibring, E. Hauber, and OMEGA Team ..............................7051

Mössbauer Spectra of Sulfates and Applications to Mars E. C. Sklute, M. D. Dyar, J. L. Bishop, M. D. Lane, P. L. King, and E. Cloutis........................................7057

Photographic Evidence for Exhumation of Light-toned Deposits from the Walls of Valles Marineris

M. R. Smith, D. R. Montgomery, A. R. Gillespie, S. E. Wood, and H. M. Greenberg ...............................7024

Overview of the Phoenix Mars Lander Mission P. H. Smith ................................................................................................................................................7069

Experimental Studies of Jarosite and Alunite at Hydrothermal Conditions R. E. Stoffregen..........................................................................................................................................7011

Workshop on Martian Sulfates as Recorders of Atmospheric-Fluid-Rock Interactions ix

Detection of Jarosite and Alunite with Hyperspectral Imaging: Prospects for Determining Their Origin on Mars Using Orbital Sensors

G. A. Swayze, G. A. Desborough, R. N. Clark, R. O. Rye, R. E. Stoffregen, K. S. Smith, and H. A. Lowers ..................................................................................................................7072

Chemical Divides and Variation in Martian Saline Mineralogy N. J. Tosca and S. M. McLennan...............................................................................................................7021

Sulfate-bearing Minerals in the Martian Meteorites A. H. Treiman ............................................................................................................................................7017

Rates and Modes of Hydration in Mg- and Ca-Sulfates on Mars D. T. Vaniman and S. J. Chipera...............................................................................................................7023

Olivine and Secondary Sulfate Minerals in Chassigny and Other Mars Meteorites: Comparison with Incipient Weathering of Terrestrial Dunitic and Basaltic Olivine

M. A. Velbel, S. J. Wentworth, and J. M. Ranck ........................................................................................7030

Hydration State of Magnesium Sulfates on Mars A. Wang, J. F. Freeman, and B. L. Jolliff..................................................................................................7040

Atmospheric Sulfur Chemistry on Ancient Mars K. Zahnle and R. M. Haberle ....................................................................................................................7046

PPPRRROOOGGGRRRAAAMMM

Sunday, October 22, 2006

POSTER SESSION 6:00 p.m. Great Room

Baldridge A. M. Christensen P. R. Detection of the Hydration Phase of Martian Sulfates Using Emission Spectroscopy of Magnesium and Calcium Sulfates [#7041] Barrón V. Torrent J. Greenwood J. P. Tranformation of Jarosite to Hematite in Simulated Martian Brines [#7052] Basilevsky A. T. Ryzhenko B. N. Abdrakhimov A. M. Differentiantial Mobility of Uranium and Thorium in Aqueous Solutions as Potential Indicator of Past Geochemical Environment on Mars [#7031] Blaney D. L. Glenar D. Maguire W. Bjoraker G. Martian Sulfate Mineralogy from Spectroscopy: Ground-based, Orbital, and In Situ Perspectives [#7035] Brown A. J. Remote Sensing of Western Australian Sulfate Deposits and Applications for Mars [#7063] Brückner J. APXS Team Sulfur on the Martian Surface: In-Situ Data from All Landing Sites [#7002] Bullock M. A. Moore J. M. Atmospheric Conditions on Early Mars and the Missing Layered Carbonates [#7068] Burger P. V. Papike J. J. Shearer C. K. Karner J. M. The Role of Fluid Chemistry and Crystallization Kinetics in Na and K Zoning in Jarosite [#7019] Chavdarian G. V. Sumner D. Y. Cracks and Fins as Evidence for Water Evaporation and Condensation Associated with Temperature Changes in Hydrous Sulfate Sands [#7008] Chipera S. J. Vaniman D. T. Carey J. W. Water Content and Dehydration Behavior of Mg-Sulfate Hydrates [#7026] Coleman M. Blaney D. Estimating Minimum Volumes of Water Involved in Formation of Sulfate Evaporite Deposits [#7047] Craig M. Cloutis E. A. Sulfate Stability Under Simulated Martian Conditions [#7013] Crowley J. K. Kargel J. S. Marion G. M. Hook S. J. Bridges N. T. Brown A. J. de Souza Filho C. R. Mixing and Re-Solution Processes Affecting Evaporite Mineral Distributions on Earth and Mars [#7056] Denson J. Chevrier V. Sears D. W. G. Sulfate Brine Stability Under a Simulated Martian Atmosphere [#7066]

1Workshop on Martian Sulfates as Records of Atmospheric-Fluid-Rock Interactions

Elwood Madden M. E. Rimstidt J. D. Lifetime of Jarosite on Mars: Preliminary Estimates [#7007] Fan C. Schulze-Makuch D. Xie H. Sulfate Formation and Its Relevence to Environmental Conditions on Early Mars [#7033] Fries M. Rost D. Vicenzi E. Steele A. Raman Imaging Analysis of Jarosite in MIL 03346 [#7060] Greenwood J. P. Gilmore M. S. Martini A. M. Blake R. E. Dyar M. D. Gilmore J. A. Varekamp J. Martian and St. Lucian Jarosite: What We Can Learn About Meridiani from an Earth Analogue [#7050] Gucsik A. Nishido H. Ninagawa K. Okumura T. Matsuda N. Kayama M. Götze J. Wilcox J. Z. Bérczi Sz. Kereszturi Á. Hargitai H. Cathodoluminescence Study of Phosphates in the Y000593 Nakhlite [#7049] Johnson A. Pratt L. M. Experimental Preservation of Amino Acids in Evaporitic Sulfate Minerals as Analogs for Surficial Processes on Mars [#7061] Johnson S. S. Zuber M. T. Grove T. L. Mischna M. A. Sulfur Solubility in Martian Mantle Melts: Impacts on the Late Noachian Atmosphere [#7038] Kochemasov G. G. Sulfates and Other Salts on the Martian Surface Have Their Source Deep in the Crust [#7016] Lane M. D. Bishop J. L. Parente M. Dyar M. D. King P. L. Cloutis E. Determining the Chemistry of the Bright Paso Robles Soils on Mars Using Multispectral Data Sets [#7025] Lefticariu L. Pratt L. M. LaVerne J. A. Ripley E. M. Radiolytic Oxidation of Pyrite: A Viable Mechanism for Sulfate Production on Mars? [#7048] Papike J. J. Burger P. V. Karner J. M. Shearer C. K. Lueth V. W. Terrestrial Analogs of Martian Sulfates: Major and Minor Element Systematics of Selected Jarosite Samples [#7009] Sklute E. C. Dyar M. D. Bishop J. L. Lane M. D. King P. L. Cloutis E. Mössbauer Spectra of Sulfates and Applications to Mars [#7057] Smith M. R. Montgomery D. R. Gillespie A. R. Wood S. E. Greenberg H. M. Photographic Evidence for Exhumation of Light-toned Deposits from the Walls of Valles Marineris [#7024] Velbel M. A. Wentworth S. J. Ranck J. M. Olivine and Secondary Sulfate Minerals in Chassigny and Other Mars Meteorites: Comparison with Incipient Weathering of Terrestrial Dunitic and Basaltic Olivine [#7030] Wang A. Freeman J. F. Jolliff B. L. Hydration State of Magnesium Sulfates on Mars [#7040] Zahnle K. Haberle R. M. Atmospheric Sulfur Chemistry on Ancient Mars [#7046]

2 LPI Contribution No. 1331

Monday, October 23, 2006

CHARACTERIZATION OF SULFATE DEPOSITS ON THE SURFACE OF MARS FROM ORBITAL DATA, PAST, PRESENT, AND FUTURE

8:30 a.m. Berkners

Chairs: Brad Jolliff John Mustard Bibring J.-P. * OMEGA Team (KEYNOTE) 30 minutes Mineralogic Diversity of Mars and Discovery of Sulfate Deposits from the OMEGA/Mars Express Investigation [#7073] Calvin W. M. * Vaughan R. G. Kratt C. Shoffner J. D. ( INVITED) Mapping Sulfates in Nevada Using Reflected, Emitted, Multi-Spectral and Hyperspectral Systems [#7029] Mustard J. F. * ( INVITED) Multi-Instrument Sulfate Detection and Mineral Stability on Mars [#7055] Mangold N. * Gendrin A. Quantin C. Gondet B. Bibring J.-P. ( INVITED) Sulfate Deposits and Geology of West Candor Chasma, A Case Study [#7039] Quantin C. * Gendrin A. Mangold N. Bibring J. P. Hauber E. OMEGA Team ( INVITED) Geology of Sulfate Deposits in Valles Marineris [#7051] Noe Dobrea E. Z. * Correlations Bewteen Sulfate and Hematite Deposits as Observed by OMEGA [#7071] Arvidson R. E. * ( INVITED) The Sedimentary Rocks Exposed in Terra Meridiani [#7043] Murchie S. * Arvidson R. Bedini P. Bibring J.-P. Bishop J. Cavender P. Choo T. Clancy R. T. Des Marais D. Espiritu R. Green R. Guinness E. Hayes J. Hash C. Heffernan K. Humm D. Hutcheson J. Izenberg N. Malaret E. Martin T. McGovern J. A. McGuire P. Morris R. Mustard J. Pelkey S. Robinson M. Roush T. Seelos F. Slavney S. Smith M. Shyong W.-J. Strohbehn K. Taylor H. Wirzburger M. Wolff M. ( INVITED) Looking Forward to CRISM [#7022] 12:30 p.m. Lunch at LPI


Monday, October 23, 2006 (continued)

SULFATE CHARACTERIZATION ACCOMPLISHED BY EARLY SURFACE MISSIONS, BY MER, AND PLANNED FOR PHOENIX AND MSL

1:30 p.m. Berkners

Chairs: Douglas Ming David Vaniman Clark B. C. * (KEYNOTE) 20 minutes Direct Chemical Analysis on the Martian Surface: A Review of Sulfur Occurrence and Interpretation from Viking to MER [#7010] Squyres S.* (KEYNOTE) 20 minutes MER Overview Morris R. V. * Athena Science Team ( INVITED) Iron Sulfates at Gusev Crater and Meridiani Planum, Mars [#7042] Smith P. H. * (KEYNOTE) 20 minutes Overview of the Phoenix Mars Lander Mission [#7069] Boynton W. V. * Ming D. W. ( INVITED) Use of the Thermal and Evolved-Gas Analyzer (TEGA) on the Phoenix Lander to Detect Sulfates on Mars [#7065] Kounaves S. P. * Young S. M. M. Kapit J. A. M. Phoenix Team ( INVITED) Dissolved Sulfate Analysis on the 2007 Phoenix Mars Scout Mission [#7020] Blaney D. L. * (KEYNOTE) 20 minutes The Mars Science Laboratory (MSL) Mission [#7034] Clegg S. M. * Wiens R. C. Dyar M. D. Vaniman D. T. Thompson J. R. Sklute E. C. Barefield J. E. Maurice S. ( INVITED) Laser Induced Breakdown Spectroscopy (LIBS) Remote Detection of Sulfates on Mars Science Laboratory Rover [#7059] Bish D. L. * Sarrazin P. Blake D. Vaniman D. Chipera S. ( INVITED) Sulfate Mineral Analysis by the CheMin XRD/XRF Instrument on MSL [#7018] Mahaffy P. R. * Franz H. B. ( INVITED) Evolved Gas Analysis on the 2009 Mars Science Laboratory [#7014]


Tuesday, October 24, 2006

RECENT ADVANCES IN THE STUDY OF TERRESTRIAL ACID SULFATE MINERALS 8:30 a.m. Berkners

Chair: Virgil Lueth Alpers C. N. * (KEYNOTE) 30 minutes Terrestrial Sulfates in an Extreme Acid Mine Drainage Environment: The Richmond Mine at Iron Mountain, California [#7064] Boston P. J. * Spilde M. N. Northup D. E. ( INVITED) Extremophile Microorganism Transformations of Sulfates and Other Sulfur Minerals in Surface and Subsurface Environments [#7070] Stoffregen R. E. * ( INVITED) Experimental Studies of Jarosite and Alunite at Hydrothermal Conditions [#7011] Landis G. P. * Rye R. O. ( INVITED) Active and Noble Gas in Terrestrial Jarosite- and Alunite-hosted Fluid Inclusions: Insights and Constraints on Formation of Martian Sulfates [#7027] Lueth V. W. * ( INVITED) Textural and Stable Isotope Discrimination of Hypogene and Supergene Jarosite and Environment of Formation Effects on 40Ar/39Ar Geochronology [#7028] Coleman M. L. * Black S. Brunner B. Hubbard C. G. McGenity T. J. Mielke R. E. Yu J.-Y. Stable Isotope Characterization of Microbially Produced Sulfate: Field Data Validation at Río Tinto of New Laboratory Culture Experiments [#7036] Bishop J. L. * Brown A. J. Parente M. Lane M. D. Dyar M. D. Schiffman P. Murad E. Cloutis E. VNIR Spectra of Sulfates Formed in Solfataric and Aqueous Acid Sulfate Environments and Applications to Mars [#7037] Swayze G. A. * Desborough G. A. Clark R. N. Rye R. O. Stoffregen R. E. Smith K. S. Lowers H. A. Detection of Jarosite and Alunite with Hyperspectral Imaging: Prospects for Determining Their Origin on Mars Using Orbital Sensors [#7072] Peterson R. C. * ( INVITED) Crystal Molds on Mars: Melting of a Possible New Mineral Species to Create Martian Chaotic Terrain [#7015] 12:30 p.m. Lunch at LPI


Tuesday, October 24, 2006 (continued)

ANALYTICAL, EXPERIMENTAL, AND THEORETICAL STUDIES OF MARTIAN SULFATE RELEVANT SYSTEMS

1:30 p.m. Berkners

Chairs: Clive Neal Charles Shearer Papike J. J. * Karner J. M. Shearer C. K. ( INVITED) Jarosite-Alunite Crystal Chemistry [#7003] Dyar M. D. * Podratz L. Sklute E. C. Rusu C. Rothstein Y. Tosca N. Bishop J. L. Lane M. D. ( INVITED) Mössbauer Spectroscopy of Synthetic Alunite Group Minerals [#7053] Treiman A. H. * ( INVITED) Sulfate-bearing Minerals in the Martian Meteorites [#7017] Herd C. D. K. * Trace Elements in MIL 03346 Jarosite: A Record of Martian Surface Processes? [#7012] Vaniman D. T. * Chipera S. J. ( INVITED) Rates and Modes of Hydration in Mg- and Ca-Sulfates on Mars [#7023] King P. L. * ( INVITED) Review of Recent Theoretical Models of Salt Sequences and Solution Compositions on Mars [#7044] Moore J. M. * Bullock M. A. Mars-Analog Brines and Evaporite Experiments: Implications for Sulfates [#7032] McLennan S. M. * Grotzinger J. P. Hurowitz J. A. Tosca N. J. Sulfate Geochemistry and the Sedimentary Rock Record of Mars [#7045] Tosca N. J. * McLennan S. M. Chemical Divides and Variation in Martian Saline Mineralogy [#7021] Lepper K. * Morken T. Podoll A. Sulfates as Geochronometers/Geodosimeters for In-Situ Mars Surface Science [#7054] Neal C. R. * ( INVITED) The Challenge of Returning Hydrated Sulfates from the Surface of Mars to Earth [#7058]


TERRESTRIAL SULFATES IN AN EXTREME ACID MINE DRAINAGE ENVIRONMENT: THE RICHMOND MINE AT IRON MOUNTAIN, CALIFORNIA. Charles N. Alpers1,1U.S. Geological Survey, California Water Science Center, 6000 J St., Placer Hall, Sacramento, CA 95819-6129, [email protected]

Introduction: The Iron Mountain mining district,

in the Klamath Mountains of northern California, is host to some of the most extremely acid mine waters ever documented and a spectacular array of associated iron-sulfate minerals [1, 2, 3]. Oxidation of massive sulfide deposits consisting of > 95 % pyrite in rhyolitic host rocks with minimal acid-neutralization potential has led to mine waters with pH values as low as –3.5 and concentrations of dissolved iron and sulfate of several molar [1]. The underground tunnels and stopes of the Richmond mine at Iron Mountain have provided a useful laboratory for improving the understanding of hydrogeochemical, mineralogical, and microbiological processes associated with sulfide mineral oxidation and the formation of iron-sulfate minerals. Some of the hydrogeochemical and mineralogical characteristics observed on a large scale within the Richmond mine may occur on a smaller scale in other settings, such as other mine drainage and mine-waste environments. Because jarosite and other iron-sulfate minerals likely occur on the surface of Mars [4, and references therein] it is useful to describe the mineralogy and geochemistry of the sulfate minerals and associated water chemistry as a possible analog to conditions that may have occurred during Martian history. Mineralogy and Water Chemistry: Table 1 lists idealized formulas for the principal iron-sulfate miner-als found in the Richmond mine in their general se-quence of formation. The oxidation of pyrite proceeds by a reaction in which ferric iron (Fe3+) is the oxidant and ferrous iron (Fe2+) is a product. As long as an acid mine water is in contact with pyrite, the dissolved Fe will remain predominantly in the ferrous state because of the strong reducing capacity of the pyrite. Rapidly flowing mine water will still maintain a high propor-tion of Fe2+ because the oxidation rate typically is slow relative to the flow rate of the water. Within the Rich-mond mine, Fe-sulfate salts containing exclusively Fe2+ (melanterite, rozenite, and szomolnokite) are found close to pyrite sources and associated with the more rapidly flowing waters. Fe3+-bearing sulfate min-erals were observed to form in more stagnant condi-tions, spatially removed from pyrite mineral surfaces [3].

The Fe–S molar ratio (Fe/S) is an important factor in determining both the acidity of weathering solutions and the mineralogy of iron-sulfate weathering prod-ucts. The excess of S in the stoichiometry of pyrite (Fe/S = 0.5) leads to abundant sulfuric acid upon oxi-dation. A systematic relation was found between the

pH of the mine water and the Fe/S of Fe3+-sulfate weathering products. Rhomboclase (Fe/S = 0.5) is as-sociated with waters of pH less than –3. Copiapite group minerals, coquimbite, römerite, and voltaite (Fe/S between 0.67 and 1.0) are associated with waters of pH between –0.9 and –2.6 [5]. Jarosite group min-erals (Fe/S = 1.5) are associated with water in the pH range 1.5 to 3 [6]. In other settings, schwertmannite [Fe8O8(OH)8-2x(SO4)x, Fe/S = 5 to 8] is associated with weathering solutions in the pH range of 3 to 5 [7].

Conclusions: Some insights into the systematics of iron-sulfate mineral formation have been gained from intial studies of the mineralogy and geochemistry of weathering products at Iron Mountain, Calfornia. Ad-ditional work on mineral solid solutions and thermo-dynamic properties of minerals and aqueous solutions are needed to develop predictive models that would be helpful in understanding mineral formation in mine drainage settings and in other environments such as the surface of Mars.

References: [1] Norstrom, D. K. and Alpers, C. N. (1999) Proceed. Nat. Acad. Sci. USA, 96, 3455–3462. [2] Nordstrom, D. K. et al. Environ. Sci. Technol., 34, 254–258. [3] Alpers, C. N. et al. (2003) Mineral. Assoc. Canada Short Course Notes, 34, 407–430. [4] King, P. L. and McSween, H. Y. Jr., JGR, 110, E12S10. [5] Jamieson, H. E. et al. (2005) Chem. Geol., 215, 387–405. [6] Jamieson, H. E. et al. (2005) Canad. Mineral. 43, 1225–1242. [7] Bigham, J. M. and Nordstrom, D.K. (2000) Rev. Mineral. Geochem., 40, Chap. 7. TABLE 1. IDEALIZED FORMULAS OF THE IRON-SULFATE MINERALS THAT OCCUR IN THE RICHMOND MINE, IRON MTN., CA Mineral Melanterite Rozenite Szomolnokite Magnesiocopiapite Römerite Coquimbite Kornelite Rhomboclase Voltaite Halotrichite– Bilinite Jarosite

Idealized Formula Fe2+SO4·7H2O Fe2+SO4·4H2O Fe2+SO4·H2O

MgFe3+4(SO4)6(OH)2·20H2O

Fe2+Fe3+2(SO4)4·14H2O

Fe3+2(SO4)3·9H2O

Fe3+2(SO4)3·7H2O

(H3O)Fe3+(SO4)2·3H2O K2Fe2+

5Fe3+4(SO4)12·18H2O

Fe2+Al2(SO4)4·22H2O – Fe2+Fe3+

2(SO4)4·22H2O (K,H3O,Na)Fe3(SO4)2(OH)6


THE SEDIMENTARY ROCKS EXPOSED IN TERRA MERIDIANI. R. E. Arvidson1, 1Washington Univer-sity, St. Louis, MO 63130, [email protected].

Introduction: In this abstract the observations ac-

quired by the Mars Exploration Rover, Opportunity [1], and the orbital data acquired by the Mars Express OMEGA hyperspectral imager for the sedimentary rocks in Terra Meridiani [2-5] are jointly analyzed, and a model is presented for the formation and modifi-cation of the deposits.

Observations: The traverses and observations completed by Opportunity show that the Meridiani plains consist of sulfate-rich sedimentary rocks that are covered by poorly-sorted basaltic aeolian sands and a lag of granule-sized hematitic concretions. Orbital spectra obtained by OMEGA over this region are dominated by pyroxene, plagioclase feldspar, crystal-line hematite (i.e., concretions), and nano-phase iron oxide dust signatures, consistent with Pancam and Mini-TES observations. Mössbauer Spectrometer ob-servations indicate more olivine than observed with the other instruments, consistent with preferential optical obscuration of olivine features in mixtures with pyrox-ene and dust.

A ~1 km vertical section of etched terrain and hematite-bearing plains materials and nearby cratered terrain surfaces was mapped in the northern portion of Meridiani Planum (~390 km to the northeast of Oppor-tunity) using OMEGA data. The oldest materials are the cratered plains, which are dominated by a mix of low and high calcium pyroxenes. Etched plains mate-rials overlie this unit and are exposed within a 120 km NW-SE trending valley to the south of the cratered plains. Lower etched plains materials exhibit a kieser-ite-like signature on a plateau-forming horizon and polyhydrated sulfate-like signatures on the main valley floor. The upper etched plains unit exhibits signatures consistent with hydrated iron oxides and is covered by a relatively thin layer of basaltic sand and hematitic concretions. The youngest unit consists of ejecta de-posits from a cluster of six craters that mantle the east-ern portion of the study area.

Model: The most plausible regional-scale model for formation of the Meridiani deposits is one in which the water table rose relative to the dissected cratered terrain surfaces, resulting from tectonic subsidence and/or enhanced recharge of the cratered terrain high-lands to the southwest. A regime of relative uplift and dissection switched to one of relative subsidence and sedimentary accumulation onto the cratered terrains. The several kilometers of relief between the cratered highlands to the northwest and the dissected cratered terrains to the southeast would have produced the hy-drostatic head necessary for regional-scale ground

water flow. In fact, regional scale modeling of ground water flow indicates that the Meridiani area would be one where ground water would upwell toward the sur-face [6]. Sulfur and other volatile species were intro-duced to the hydrologic system as a consequence of extensive volcanism from Tharsis (and other) volca-noes and/or by weathering of pre-existing sulfur-bearing deposits and would have produced an acid-sulfate ground water system.

Relative rise of the groundwater table resulted in the development of springs and playa lakes of high ionic strength within local topographic depressions. Desiccation of these local, shallow water bodies would have provided a ready source of “dirty evaporite” de-posits dominated by sulfates and weathered siliciclastic components. Evaporation of pore fluids within the capillary fringe, or surface water within playa lakes, would have precipitated evaporite minerals as cements that bound siliciclastic grains together [7,8]. During dry periods, erosion and redistribution of these ce-mented mudstones would have occurred by aeolian processes and during wetter periods by water flow. Preservation would have been assured as the ground water table continued to rise, with associated diagenetic processes and cementation of deposits within the capillary fringe. New evaporite and related deposits would have continued to accumulate at the depositional surface as the water table continued to rise, and rose to form shallow pools that became evaporitic playas.

After the Meridiani hydrologic system ceased op-erating, aeolian processes would have taken over as the dominant process. The modern Meridiani plains formed via wind erosion of the sulfate-dominated sedimentary deposits, and accumulation of a thin ve-neer of aeolian basaltic sand advected into the region. Hematitic concretions formed as lag deposits as the softer sulfate rocks were eroded by wind. Occasional sulfate outcrops were exposed via cratering and in-between aeolian ripples, where the basaltic sand cover is thinnest.

References: [1] Squyres S. W. et al. (2006) JGR, submitted. [2] Arvidson R. E. et al. (2005) Science, 307, 1591-1594. [3] Bibring J. -P. (2005) Science, 307, 1576–1581. [4] Arvidson R. E. et al. (2006) JGR, in press. [5] Griffes, J. L. et al. (2006) JGR, in press. [6] Hanna J. C. and Phillips R. J. (2006) LPS XXXVII, Abstract #2373. [7] Grotzinger J. P. et al. (2005) EPSL, 240, 11-72. [8] McLennan S. M. et al. (2005) EPSL, 240, 95-121.


Detection of the Hydration Phase of Martian Sulfates Using Emission Spectroscopy of Magnesium and Cal-cium Sulfates. A. M. Baldridge1 and P. R. Christensen1, 1School of Earth and Space Exploration, Arizona StateUniversity, M.C. 6305, Tempe, AZ, 85287-6305 [email protected].

Introduction: Orbital data at Mars suggest the oc-currence of near surface water [1-3]. The hydrationmay be associated with hydrated sulfate species ob-served in situ and by orbital measurements. OMEGAdata as well as modeling of APXS chemistry [4], andlinear unmixing of the mini-TES data [5] from theMars Exploration Rovers at Meridiani, suggest bothcalcium and magnesium sulfates are present. Detailedanalysis of the outcrop spectra at Meridiani [6] suggestthe presence of gypsum and kieserite. However, thelibraries for deconvolution of mini-TES include only afew hydration states of magnesium and calcium sul-fates. We have added to the library a complete suite ofhydration states for both of these sulfate groups. Wehave applied these new spectral data to the deconvolu-tion of the martian outcrop spectra to better under-stand the sulfate chemistry and hydration state

Methods: Magnesium sulfate powders were pre-pared by S. Chipera for this study using techniquesdescribed in [7, 8] . The minerals were analyzed withXRD at both ASU and LANL to verify chemistry,structure and hydration state. Powders were pressedinto pellets to decrease scattering and thermal infraredspectra were acquired at Arizona State University’sThermal Emission Spectroscopy Laboratory at ambientpressure. Mineralogical analysis was performed usingthe linear deconvolution method of [9]. A library ofendmembers was selected following [6] and adding thefull suite of Mg-sulfates.

Results: Emissivity spectra for the sulfate samplesare shown in Figure 1. The position of the absorptioncorresponding to the v3 S-O asymmetric stretch shiftsto higher energy with decreasing number of boundwaters. This shift has been noted by [10] in emissivitystudies as well as by [11, 12] in Raman spectral stud-ies. Variations in water content give rise to changes inthe crystal structure of sulfates [13] as well as changein energy of the bonds between water and the SO4 tet-rahedra groups and between SO4 and the MgOn(OH2)6-n

octahedral resulting in the shift of absorption featureswith mineral hydration.

The deconvolution results using the library andconstraints of [6] and the library that includes the fullsuite of sulfates are shown in Figure 2. The differencesbetween this study and [6] include the increased abun-dance of jarosite and the lack of nontronite. The detec-tion of multiple hydration states of both Mg- and Ca-sulfates is not unexpected [8, 14-16]. Use of the sul-fates improves both the fit and the RMS error previ-ously derived by [6].

Figure 1.

Figure 2.

References: [1] Feldman, W.C., et al. (2002) Science, 297(5578)75-78. [2] Calvin, W.M. (1997) Journal of Geophysical Research-Planets, 102(E4) 9097-9107. [3] Baldridge, A.M. and W.M. Calvin(2004) Journal of Geophysical Research-Planets, 109(E4) -. [4]Rieder, R., et al. (2004) Science, 306(5702) 1746-1749. [5] Christen-sen, P.R., et al. (2004) Science, 306(5702) 1733-1739. [6] Glotch,T.D., et al. (submitted) Journal of Geophysical Research - Planets.[7] Chipera, S.J., et al. (2005) LPS XXXIIIVI, Abstract #1497. [8]Chipera, S.J., et al. (2006) LPS XXXVII, Abstract #1457. [9] Ram-sey, M.S. and P.R. Christensen (1998) Journal of Geophysical Re-search-Solid Earth, 103(B1) 577-596. [10] Lane, M.D. (submitted)American Mineralogist. [11] Chio, C.H., et al. (2004) AmericanMineralogist, 89(2-3) 390-395. [12] Wang, A., et al. (2006) 37thAnnual Lunar and Planetary Science Conference, 2191. [13] P.H.Ribbe, (2000), Sulfate minerals : crystallography, geochemistry, andenvironmental significance. [14] Vaniman, D.T., et al. (2005) LPSXXXIIIVI, Abstract #1486. [15] Vaniman, D.T., et al. (2006) LPSXXXIIIVII, Abstract #1442. [16] Vaniman, D.T., et al. (2004) Nature,431(7009) 663-665.

0.8

0.85

0.9

0.95

1

1.05

400 600 800 1000 1200 1400

Wavenumber (cm-1)

Glotch et.al this studySilica/Glass 25% 18%Nontronite 10% ---Jarosite 10% 28%Mg-Sulfate 20% 21%Ca-Sulfate 10% 14%Plagioclase 15% 8%Fe-Oxides 5% 6%Other 5% 5%RMS% 0.307 0.282

derived outcrop spectrummodeled spectrum

0

0.5

1

1.5

2

400 600 800 1000 1200 1400

Wavenumber (cm-1)

Anhydrous

Kieserite_a

Kieserite_b

Sanderite

Starkeyite

Pentahydrite

Hexahydrite

Anhydrite

Bassanite

Gypsum


TRANSFORMATION OF JAROSITE TO HEMATITE IN SIMULATED MARTIAN BRINES. V. Barrón1, J.

Torrent1, and J. P. Greenwood

2,

1 Universidad de Córdoba, Edificio C4, Campus de Rabanales, Córdoba, Spain,

2Dept. of Earth & Environmental Sciences, Wesleyan University, Middletown, CT 06459.

Jarosite [KFe3(OH)6(SO4)2], a pale yellow mineral,is a common product of the oxidation of iron sulfidesin acidic environments, such as sulfuric soil horizonsand acid mine drainage. Jarosite has recently attractedmuch attention because it has also been identified inthe evaporitic deposits of Mars. Here, we report thehydrolysis products of synthetic K-jarosite at differentpH, temperature, and phosphate and salt concentrationsby X ray diffraction, diffuse reflectance spectroscopy,scanning and transmission electron microscopy, andchemical analysis. We synthesized jarosite by first dis-solving 0.1 mol of Fe2(SO4)3, 0.4 mol MgSO4, 0.04mol of AlCl3, 0.06 mol of Na2SO4, 0.002 mol of CaCl2,0.004 mol of MnSO4 and variable amounts ofKH2(PO4) in 160 mL of de-ionized water. A concen-trated solution of KOH was then added to reach a pHof 2 and a volume of 220 mL before shaking the re-sulting suspension at room temperature for two weeks.At this time, the solids in the suspension consisted ex-clusively of jarosite. In a factorial experiment, portionsof the suspension were then mixed with saline solu-tions of the same ionic composition as the one used inthe synthesis [except for Fe(III) and PO4] and water atdifferent proportions so that the resulting electricalelectrical conductivity (EC) of the suspension (firstfactor) was either 60, 20 or 1 mS/cm. The pH (second

factor) was raised to 4, 6 or 8. Finally, the suspensionswere aged for 6 months at a temperature (third factor)of either 303 or 333 K. During aging, pH and salt con-centration were periodically adjusted to the target val-ues. High salt concentration inhibited the transforma-tion of jarosite except at pH 8 (Figure 1), suggestingthat jarosite is stable even at circum-neutral pH if wa-ter activity is sufficiently low. Nanophase hematitewas the most common product of the transformation ofjarosite, particularly when salt and phosphate concen-trations were high. Nanogoethite was formed onlywhen salt concentration was low (i.e., at high wateractivity) and pH was 6, and was never an intermediatephase in the transformation from jarosite into hematite.At pH 8 jarosite was converted rapidly (<7 days) to 2-line ferrihydrite then evolved, with time, to hematite orto a mixture of 2-line ferrihydrite and nano-lepidocrocite.

Implications for Meridiani: Direct tranformationof jarosite to hematite is possible without intermediateformation of goethite or poorly crystalline iron oxyhy-droxide phases at low pH in short time. With highPO4, the jarosite-goethite transformation at circum-neutral pH is suppressed and jarosite can transformdirectly to hematite as well. This implies a very tran-sient fluid system after jarosite formation at Meridiani.


DIFFERENTIANTIAL MOBILITY OF URANIUM AND THORIUM IN AQUEOUS SOLUTIONS AS POTENTIAL INDICATOR OF PAST GEOCHEMICAL ENVIRONMENT ON MARS. A. T. Basilevsky, B. N. Ryzhenko, and A. M. Abdrakhimov. Vernadsky Institute of Geochemistry and Analytical Chemistry, RAS, Moscow 119991 Russia ([email protected]). Introduction: Recent orbital (1, 2) and on-surface (3, 4) studies of Mars accompanied by thermodynamical calculations (e.g., 5) provided evidence that in Late Noachian-Hesperian time the surface environment on Mars allowed to form Mg, Ca and Fe+3 (jarosite) sulfates as well as “grey” hematite suggesting deposition in acidic water of shallow lakes under oxidizing conditions. The Opportunity observations showed that aqueous environment was alternating in time with aeolian one probably suggesting wetter and dryer periods [3]. The gamma-ray mapping by the Mars Odyssey orbiter [6, 7] has provided data on contents of thorium (and a number of other elements) in the surface materials of this planet and will expectedly provide the data on uranium contents as well. In this work we explore possibility of differential mobility of uranium and thorium in aqueous solutions under different pH and Eh conditions during the sulfate-formation period of the geologic history of Mars that may provide additional information on exogenic geochemical processes of that time. The calculations results: We have done the multi-component thermodynamic modeling using the GIBBS computer code (8, 9) calculating Th and U contents in the aqueous solution resulting from interaction of water with different additions of H2SO4 with Th-U-bearing rock (average mafic [10]) containing thorianite and uranium minerals (chosen depending on Eh). The modeling was done for T = 25C, P = 1 bar and oxygen fugacity from 1 to 10 exp -60 (g = 0 to -60) (Figure 1).

Figure 1. Diagram showing changes in U/Th ratio in the model solutions as a function of pH and Eh.

It can be seen from Figure 1 that with increasing acidity of the reacting solution and decreasing oxygen

fugacity the U/Th ratio in the resulting solution changes: At pH = 4 to 5 and Eh = 0.5 to 1, U is more soluble and the resulting solutions are highly U-enriched. Further addition of H2SO4 leads to decrease in pH and Eh and the uranium prevalence in the solution decreases. At pH being in between 2 and 3 and Eh close to 0.35-0.4 the resulting U/Th ratio is close to 1. Further addition of H2SO4 leads to decrease in pH and Eh making Th to be more soluble and prevailing in the solution. Discussion and conclusion: The modeling results suggest that most of the explored pH/Eh combinations have to lead to noticeable deviations from U/Th ≈ 0.3 ratio, which is typical for majority of igneous rocks and meteorites [11]. In the modeled sulfate era surface environment three alternatives could be: 1) The resulted solutions could migrate downward leaving behind the leached residuals like it happens in podzol environment of Earth; 2) The resulted solutions could migrate upward bringing the dissolved material closer to the surface like it happens in salinization of soils in arid environments of Earth; and 3) The resulted solutions stay stagnant intimately mixed with the altered rock. In the cases 1 and 2, surface material should have a U/Th ratio changed comparing to the initial rock. In the case 3, the U/Th ratio stays unchanged. It also has to stay unchanged if the rock-water chemical interaction is not effective. We believe that the U/Th ratios provided by the Mars Odyssey gamma-ray survey [6, 7] will show whether the U/Th ratio in different areas of the planet deviates from canonical ~0.3 or not. This in turn could be analyzed in terms of geochemical processes in different surface environments.

We are working now on modeling of interaction of water with Th-U-bearing rock at neutral (pH = 7) environment, which probably took place in the earlier ”phyllosilicate” era [1, 2]. References: [1] Poulet F. et al. (2005) Nature, 438, 623–627. [2] Bibring J.-P. et al. (2006) Science, 312, 400-404. [3] Sqyires S. W. (2004) Science, 306, 1709–1714. [4] Wang A. (2006) JGR, 111, E02S17. [5] Zolotov M. Y. and Shock E. L. (2005) GRL, 32, L21203. [6] Taylor G. G. et al. (2003) LPSC XXXVII, # 2004. [7] Taylor G. G. et al. (2006) JGR (in press). [8] Shvarov Y. V. (1999) Geochem. International, 37, 571-576. [9] Ryzhenko B. N. and Krainov S. R. (2002) Geochem. International, 40, 779-806. [10] Bogatikov O. A. et al. (1987) Mean average compositions of igneous rocks, Nedra. [11] Taylor S. R. and McLennan S. M. (1985) The Continental Crust, Blackwell.


MINERALOGIC DIVERSITY OF MARS AND DISCOVERY OF SULFATE DEPOSITS FROM THE OMEGA/MARS EXPRESS INVESTIGATION. J-P. Bibring1 on behalf of the entire OMEGA team, 1Institut d’Astrophysique Spatiale (IAS), Orsay, France, [email protected]

Introduction: OMEGA is the VIS/NIR hyper-

spectral imager operating on board the ESA Mars Ex-press mission since January 2004 [1], [2]. It maps the surface and atmosphere of Mars with a footprint vary-ing from 300m to 5 km depending on the observation altitude. To date, most of the surface has been mapped once at a 2-5 km resolution, while selected areas amounting to 5% have been covered at < 450m. OMEGA acquires the spectrum of each resolved pixel in 352 contiguous spectral channels from 0.35 to 5.1 µm. The spectral domain chosen is dominated by solar reflectance (with minor contribution from thermal emission up to 3.5 µm) and contains diagnostic signa-tures of a variety of atmospheric and surface species.

Detected constituents: Atmospheric gases (CO2, CO and H2O primarily, O2 and O3 marginally) [3], [4], clouds (CO2, H2O), and aerosols have been detected and mapped as a function of time. Frosts and ices (CO2, H2O) [5], [6], [7], have been detected and their extension monitored over a complete Martian year. OMEGA has identified both mafic and altered surface minerals [8]. More specifically, pyroxene (orthopyrox-ene and clinopyroxene) and olivine (forsterite to faya-lite) have been discriminated [9], as well as: anhydrous ferric oxides [10], hydrated phyllosilicates [11] and hydrated sulfates [12], [13], [14].

The majority of phyllosilicates are Mg/Fe smec-tites; some Al-rich ones have also been identified. Among the hydrated sulfates, kieserite (MgSO4, H2O) and gypsum (CaSO4, 2H2O) have been detected, as well as other polyhydrated ones, for which a more spe-cific composition could not be assessed yet.

It is important to note that a number of minerals cannot be unambiguously identified by OMEGA, such as the non Fe-bearing silicates (e.g. feldspar), and an-hydrous sulfates. On the other hand, OMEGA could detect carbonates, if present at levels down to a few wt%; so far OMEGA did not detect carbonates.

Mapping of surface minerals: Some of the de-tected minerals are spread over wide units: pyroxene are present in the ancient cratered terrains, in contrast with the more recent Northern lowlands in which an-hydrous (nanophase) ferric oxides dominate. Most other altered minerals, including hydrated phyllosili-cates and sulfates, have been detected in a restricted number of localized areas only. The geomorphological context of these sites, when studied through optical (MOC, HRSC) and thermal IR (TES, THEMIS) data, shows systematic trends for the emplacement of the

various minerals. Phyllosilicates are found in the most ancient terrains, exposed by either impact or erosion; the two main areas are located within i) the Nili Fossae region and ii) the Marwth Vallis. Hydrated sulfates have been found primarily in three units: within ILDs of Valles Marineris, within Terra Meridiani, and within the dark dunes of the Northern polar cap. Sul-fates in Terra Meridiani and Valles Marineris are often coupled to ferric oxides (although not always at a pixel size).

Implication for Mars History: Phyllosilicates re-cord an early era during which liquid water was likely present and stable over geological timescales, either at the surface or in the subsurface. The large occurrence of Mg/Fe smectites indicates a non acidic environment, as one would expect from an aqueous alteration of basaltic rocks. Sulfates are found in terrains formed later, some of which requiring much more acidic fluids to precipitate. On the other hand, sulfate formation does not require liquid water to remain stable over long durations. The Mars global environment seems to have drastically changed between the era when phyl-losilicates could form (phyllosian) and that of sulfate formation (theiikian) [10]: in the latter, the atmosphere could no longer sustain surface liquid water at a global scale. Sulfates would record the areas where surface water was supplied, possibly along sequences of tran-sient episodes, following the Valles Marineris opening and the tilt of Terra Meridiani, both triggered by the building of Tharsis. The coupled outgassing provided massive amounts of sulfur all over the planet, ending with a reduced surface pH. Study of Martian sulfates (composition, hydration level, formation, context), have thus a huge potential to contribute to deciphering the early History of Mars and the role water might have played.

References: [1] Chicarro A. et al. (2004), ESA SP 1240, 3-13. [2] Bibring J-P. et al. (2004), ESA SP 1240, 37-49. [3] Encrenaz T. et al. (2005) Astron. Astrophys. 441, L9-L12. [4] Encrenaz T. et al. (2006) Astron. Astrophys. in press. [5] Bibring J-P. et al. (2004), Nature 428, 627-630. [6] Langevin Y. et al. (2005) Science 307, 1581-1584. [7] Langevin Y. et al. (2006) Nature, in press. [8] Bi-bring J-P. et al. (2005) Science 307, 1576-1581. [9] Mustard J. F. et al. (2005) Science 307, 1594-1597. [10] Bibring J-P. et al. (2005) Science 312, 400-404. [11] Poulet F. et al. (2005) Nature 438, 623-627. [12] Gendrin A. et al. (2005) Science 307, 1587-1591. [13] Arvidson R. E. et al. (2005) Science 307, 1591-1594. [14] Langevin Y. et al. (2005) Science 307, 1584-1586.


SULFATE MINERAL ANALYSIS BY THE CHEMIN XRD/XRF INSTRUMENT ON MSL. D. L. Bish1, P. Sarrazin2, D. Blake3, D. Vaniman4, and S. Chipera4, 1Dept. of Geol. Sci., Indiana Univ., 1001 E. 10th St., Blooming-ton, IN 47405-1405, [email protected]; 2inXitu, Mountain View, CA 94042; 3NASA Ames Research Center, Moffett Field, CA 94035; 4Los Alamos Nat. Lab., Los Alamos, NM 87545.

Introduction: The presence of sulfate minerals on

Mars has been inferred since the discovery of an Mg-S correlation in Viking X-ray fluorescence data [1]. The existence of Mg-sulfates on Mars was bolstered by Pathfinder [2,3] and by MER chemical, thermal emis-sion spectroscopy, and Mössbauer data [4,5,6]. Recent OMEGA hyperspectral images have identified hy-drated sulfates, including gypsum or bassanite, “poly-hydrated sulfates,” and kieserite [7]. Of these miner-als, with the exception of jarosite, identified by Möss-bauer spectroscopy [6], and the OMEGA kieserite identification [7], mineral identifications are typically somewhat ambiguous and alternate identifications are usually possible. Inferences about past conditions can be made from the presence of specific minerals [8], and accurate mineralogic data are particularly crucial to constrain stability and genesis. Diffraction data typically provide unambiguous mineral identification, even in mixtures or for compositionally very similar materials such as gypsum and bassanite (Fig. 1).

0

20

40

60

80

100

120

0 10 20 30 40 50 602-theta

Inte

nsity

BassaniteGypsum

Figure 1. Calculated XRD patterns for bassanite

(CaSO4•½H2O) and gypsum (CaSO4•2H2O) (Co Kα).

Methods: CheMin is a miniaturized X-ray diffrac-tion/X-ray fluorescence (XRD/XRF) instrument that is part of the MSL payload. It uses a Co X-ray source with an angular range of ~2 to 60º 2θ and operates in transmission mode with a vibrated specimen, yielding partial to full Debye rings. These features compensate for poor particle statistics and preferred orientation.

Specimen Transparency: Total diffracted inten-sity for a beam perpendicular to a specimen is ID = [a*b*t*I0/(cosθ)] e-µ t /cosθ , where a = volume fraction of the specimen oriented for diffraction; b = fraction of the incident energy diffracted, t = specimen thickness, and µ = linear absorption coefficient. With this equa-

tion, we see that Id is a maximum when t = 1/µ, so it is important to minimize µ. Fe-bearing minerals are problematic with Cu radiation because of their high values of µ, and CheMin’s use of a Co X-ray tube in-creases transmission for Fe-minerals by at least a fac-tor of two [e.g., µ values for hematite, Fe2O3, are 1150.2 cm-1 (Cu) vs. 222.2 cm-1 (Co)]. For Co radia-tion, the transmission factor for 100-µm thick jarosite (KFe+3

3(SO4)2(OH)6) is 0.15 and the intensity falls off to 1/e at 53 µm (compared with 25 µm for Cu radia-tion). The transmission factor for 100-µm thick bot-ryogen (MgFe+3(SO4)2(OH)·7H2O) is ~0.4 and the intensity falls off to 1/e at 110 µm. The transmission factor for 100-µm thick gypsum (CaSO4

.2H2O) is ~0.11, and the intensity falls off to 1/e at 45 µm. These values are for theoretical densities, and powder speci-mens in CheMin will have fractions of these values, yielding much more transparent powders. A sample cell thickness for CheMin of 175 µm allows acceptable transmission values for all expected minerals; Figure 2 illustrates a CheMin-measured XRD pattern of a mix-ture of three sulfate minerals.

Figure 2. CheMin III diffractogram of a jarosite-kieserite (MgSO4

.H2O)-hexahydrite (MgSO4.6H2O) mixture. Col-

ored bars show maxima for each mineral (inset: quanti-tative Rietveld analysis, nominally 33% of each mineral).

References: [1] Toulmin P. et al. (1977) JGR, 82,

4625-4634. [2] Wänke H. et al. (2001) Space Sci. Rev., 96, 317-330. [3] Foley C. N. et al. (2003) JGR, 108, 8096. [4] MER Rover web site (2004) www.jpl.nasa.gov/mer2004/rover-images/mar-02-2004/images-3-2-04.html. [5] Brueckner, J. (2004) EOS Trans. AGU, 85(17), V11A-05. [6] Klingelhöfer, G. (2004) Science, 306, 1740-1745. [7] Gendrin A. et al. (2005) Science, 307, 1587-1591. [8] King P. L. et al. (2004) Geoch. Cosmoch. Acta, 68, 4993-5008.

Kieserite 38%Hexahydrite 30%Jarosite 32%


VNIR SPECTRA OF SULFATES FORMED IN SOLFATARIC AND AQUEOUS ACID SULFATE ENVIRONMENTS AND APPLICATIONS TO MARS. J. L. Bishop1, A. J. Brown1, M. Parente2, M. D. Lane3, M. D. Dyar4, P. Schiffman5, E. Murad6 and E. Cloutis7. 1SETI Institute/NASA-Ames Research Center, Mountain View, CA, 2Stanford University, Packard Engineering Building, Stanford CA, 3Planetary Science Institute, Tucson, AZ, 4Mount Holyoke College, South Hadley, MA, 5Dept. of Geology, Univ. of Calif., Davis, CA, 6Bayerisches Landesamt, Marktredwitz, Germany, 7Univ. of Winnipeg, Canada. ([email protected])

Sulfates formed in solfataric and aqueous acid

sulfate environments on Earth can provide information about current and former environments on Mars. VNIR lab spectra of sulfate minerals and sulfate-bearing rocks and soils are being compared with current Mars spectral datasets. New tools currently being finalized for processing and identification of Pancam, OMEGA (and CRISM) images enable global mapping of sulfates in these Martian image cubes.

Lab Spectra of Sulfates from Mars Analog Sites: We have been collecting and measuring spectra of a variety of sulfate minerals and sulfate-bearing samples from solfataric and aqueous acid sulfate environments in order to provide compositional information on the jarosite and other sulfates observed in Martian spectra.

Jarosite Family. One project involves a collection of jarosite and alunite samples from many locations plus several synthetic ones and builds on a recent study [1]. These together span a range of Fe and Al values and K, Na and H3O abundances.

References: [1] Bishop & Murad (2005) American Mineralogist, 90, 1100, [2] Bishop et al. (2005) LPS XXXIV, Abstract #1456, [3] Bishop et al. (2006) LPS XXXV, Abstract #1423 [4] Bishop et al. (1998) JGR, 103, 31,457, [5] Bishop & Murad (1996), in Mineral Spectroscopy, (Geochem. Soc.) 337, [6] Bishop et al. (2005) IJA, 3, 275, [7] Lane et al. (2004) GRL, 31, L19702, [8] Cloutis et al. (2006) Icarus, 184, in press.

Solfataric Sites. Samples from an acid-fog type weathering environment in Kilauea contain jarosite (orange layer) and gypsum (white layer) [2]; samples collected near a cinder cone at Haleakala contain alunite and jarosite [3]; a sample from an active vent at Santorini contains alunite and alunogen [4].

Aqueous Acid Sulfate Sites. Low pH environments,

such as acid rock drainage sites, produce a variety of sulfate minerals: e.g. schwertmannite [5] and rozenite [6], ferricopiapite and coquimbite [7] and others [8].


The Mars Science Laboratory (MSL) Mission. D. L. Blaney, NASA Jet Propulsion Laboratory, California Insti-tute of Technology, MS 183-501, 4800 Oak Grove Drive, Pasadena, CA 91109, email: [email protected].

Introduction: The MSL mission will be the first chance to follow up in situ on the wealth of new in-formation on Martian sulfates that has emerged over the last several years. MSL will bring to bear a power-ful suite of analytical, remote sensing, and environ-mental instrumentation on a capable, long-lived rover with a flexible sample acquisition and processing ca-pability. This talk will provide an overview of the MSL mission and how it might answer key questions about Martian sulfates. An emphasis will be placed on the payload and how the various instruments work together with the rover to accomplish the MSL science objectives.

Mission Overview: MSL launches in Sept 2009 and arrives on Mars between July and October 2010. The MSL rover can land at elevations up to +1.0 km (Mars Orbiter Laser Altimeter [MOLA]) with a land-ing accuracy of 10 km (radial) between ±45° latitude. MSL will operate on the Martian surface for 1 Mars year (669 sols/687 days). The rover is capable of traveling up to 20 km distance and collecting 74 sam-ples of rock and regolith.

Science Objective: The primary scientific goal of the MSL project will be to deploy to the surface of Mars a mission equipped with the capability to assess the present and past habitability of the Martian envi-ronments. An assessment of present habitability re-quires an evaluation of the characteristics of the envi-ronment and the processes that influence it from mi-croscopic to regional scales and a comparison of these characteristics with what is known about the capacity of life as we know it to exist in such environments. The determination of past habitability has the added requirement of inferring environments and processes in the past from observation in the present. Such as-sessments require integration of a wide variety of chemical, physical, and geological observations with the full range of instruments that comprise the MSL payload. These goals are very compatible with inves-tigating sulfates on Mars due to the pervasiveness of sulfates as an indicator of aqueous processes on Mars.

Payload: The MSL Science Payload consists of 10 instruments that are provided by a combination of U.S. and international Principal Investigators (PI).

• Mast Camera (MastCam), PI M. Malin, MSSS: Color stereo and multispectral imaging for geo-morphology and atmospheric opacity.

• Mars Hand Lens Imager (MAHLI), PI K. Edgett, MSSS: Color hand lens imaging for rock and soil texture.

• Mars Descent Imager (MARDI), PI M. Malin, MSSS: Imaging during descent.

• Alpha Particle X-Ray Spectrometer (APXS), PI R. Gellert, U of Guelph (Canada): Chemical com-position of contact surface.

• Chemistry & Camera (ChemCam), PI R. Wiens, LANL: Remote chemical composition and im-aging.

• Chemistry & Mineralogy X-Ray Diffrac-tion/X-Ray Fluorescence Instrument (CheMin), PI D. Blake, NASA ARC, Mineralogy and chemical compo-sition of samples.

• Sample Analysis at Mars Instrument Suite with Gas Chromatograph, Mass Spectrometer, and Tunable Laser Spectrometer (SAM), PI P. Mahaffy, NASA GSFC: Chemical and isotopic composition (incl. organic molecules) of samples and atmospheric gas.

• Radiation Assessment Detector (RAD), PI D. Hassler , SwRI: High-energy radiation.

• Dynamic of Albedo Neutrons (DAN), PI I. Mitrofanov, IKI (Russia): Subsurface hydrogen abun-dance / distribution.

• Rover Environmental Monitoring Station (REMS), L. Vazquez, CAB / CRISA (Spain): Meteor-ology / UV radiation

Rover Capabilities: The MSL rover will be able to drive up to 20 km which will provide it the capabil-ity to drive up to landforms on the edge of the 10 km landing ellipse. This will allow access to material that is too rough to land in but is of high scientific interest. The rover also can abrade and/or brush surfaces and place and hold contact instruments (MAHLI and APXS) on rocks and soils. Samples of rock or re-golith can be acquired via coring device or scoop. Once acquired, rock cores, small pebbles, or regolith into are processed into smaller particles and deliver the processed material to the analytical lab instruments (SAM and CheMin).

Landing Site: Landing site selection will also play a vital role in the success of MSL mission. MSL landing site selection involves inputs from the entire Mars community. The first workshop was held May 31-June 2, 2006. At this workshop a wide range of landing sites were discussed and prioritized. Sulfate rich sites were widely recognized as important and were prioritized as high priority for added study and information.


Martian Sulfate Mineralogy from Spectroscopy: Ground-Based, Orbital, and In Situ Perspectives. D. L. Blaney1, D.. 2Glenar2, W. Maguire2 , G. Bjoraker2 . 1NASA Jet Propulsion Laboratory, California Institute of Tech-nology, MS 183-501, 4800 Oak Grove Drive, Pasadena, CA 91109, email: [email protected]. 2NASA Goddard Space Flight Center, Solar System Exploration Division, Code 693, Bldg 2, Rm S107.

Overview: New ground based data can be used to determine sulfate mineralogy in the 4-5μm region. This data complements existing orbital and in situ data and can be used to investigate the origin of sulfates in the bright soils of Mars.

Prespectives from In Situ and Orbital Data: Recent results from NASA’s Mars Exploration Rovers (MER) and the ESA Mars Express OMEGA investiga-tion have demonstrated the widespread role of sulfate minerals as the key marker in aqueous / chemical proc-esses on Mars. The Spirit rover confirmed earlier discoveries by Viking and Pathfinder that sulfates are generally enriched in the Martian crust (e.g. Squyres et al. 2004a, Reider et al. 1997,Clark et al. 1982) with sulfate abundances ranging from 5-15%. Meanwhile, the Opportunity rover found extensive magnesium sulfate rich deposits associated with aqueous sedi-ments (e.g. Squyres et al. 2004b).

Orbital remote sensing of sulfates has provided a new perspective on the surface sulfate distribution but has also left major unanswered questions. Recently, OMEGA has detected large localized deposits of sev-eral hydrous sulfate mineral deposits (gypsum, kieser-ite, hydromagnesite) in the 1-2.5 µm region (e.g. Bi-bring et al. 2005, Langevin et al. 2005, Gendrin et al 2005). These sulfates have been mapped and are clearly associated with specific geologic locations (e.g. intercrater layer deposits in Valles Marineris and other locations, the North polar sand sea gypsum deposit) and are not the sulfates associated with bright soils and duracrust formation. The sulfate bands mapped by OMEGA are due to water in sulfate minerals but these sulfates also have features at longer wavelengths.

The sulfur content of Martian bright soils at the Viking I, II, and Pathfinder sites is higher than the sulfur content of basaltic rocks which provide the original starting material for Martian soils. Thus sulfur (and other salts) must be incorporated into the soils by chemical processes.

Two types of processes have been proposed for the incorporation of sulfates into Martian soils: aqueous and atmospheric. Determination of the mineralogy of the sulfates in martian bright soils and maps of the regional distribution of sulfates may allow us to distin-guish between potential sources of sulfates and their mode of origin.

Background: In Blaney and McCord, (1995) it was shown that the rise out of the 4.2 µm 4.4 µm CO2

band on Mars cannot be matched solely by atmos-pheric gas constituents. An absorption must be added at roughly 4.5 µm in order to decrease the reflectance rise and produce the 4.5 µm inflection present in the data. The location of this feature at the 2ν3 overtone of the SO4

-2 anion indicated that the surface absorption is caused by sulfates on the Martian surface and/or in atmospheric dust. An exact match to a terrestrial sul-fate mineral was not made but it was suggested that the mineral has very weak structure and thus a high degree of symmetry.

The shape of the surface sulfate feature should be sensitive to both sulfate species and concentration, but this information is suppressed by interference from the overlying atmosphere. The 4.5-5 µm wavelength re-gion on Mars is spectrally very complex. In addition to surface absorptions, the Martian atmosphere be-tween 4.4 - 5.1 µm contains numerous absorption bands from CO2, CO, and O3. Both reflected solar and thermal emission from surface and atmosphere con-tribute significantly at these wavelengths. Kirchoff’s law (emissivity = 1-reflectance) can provide patho-logic cases where (depending on the surface tempera-ture) mineralogical absorption features can be filled in by thermal emission. Thus Mars spectra in this region will require careful modeling to interpret successfully.

New Ground Based Data: On Oct 25, 2005 we obtained multiple spectral image cubes spanning this wavelength range using SPEX at the NASA Infrared Telescope Facility. This high quality data set permits us to explore sulfate mineralogy globally and region-ally via a combination of forward modeling and least-squares retrievals, utilizing new laboratory measure-ments of sulfate minerals. Additional constraints are imposed by existing compositional data sets (orbital, in situ, and ground-based). We summarize the results of our ongoing analysis of this data set.

This work is being carried out at the Jet Propulsion Laboratory, California Institute of Technology, under con-tract to NASA. References: Bibring JP,et al. (2005) Science 307 1576-1581. Bibring,JP, et al (2006)Science 312, 400-404. Blaney and McCord, (1995), J. Geophys. Res.100, 14433-14441. Clark et al., (1982), J. Geo-phys. Res., 87, 10,059 10,068. Gendrin A et al.(2005), Science, 307, 1584. Rieder R. et al., (1997),Science, 278, 1771-1778.Squyres, S. W. et al. (2004a), Science 305, 794–799. Squyres, S. W. et al. (2004b), 306, 1698–1703.


EXTREMOPHILE MICROORGANISM TRANSFORMATIONS OF SULFATES AND OTHER SULFUR MINERALS IN SURFACE AND SUBSURFACE ENVIRONMENTS. P.J. Boston1, M.N. Spilde2, and D.E. Northup3, 1Dept. Earth & Environmental Sci., New Mexico Tech., 801 Leroy Place, Socorro, NM 87801, [email protected], 2Inst. Meteoritics, Univ. New Mexico, Albuquerque, NM 87131, [email protected], 3Biol. Dept., Univ. New Mexico, Albuquerque, NM 87131, [email protected]

Introduction: Numerous active sulfur transform-

ing organisms live in sulfur rich environments in both Earth’s surface and subsurface. Amongst those that our team has studied are organisms in a sulfuric acid dominated cave system that aid in precipitation of sul-fates [1] (Fig. 1), microbial communities in a briny sulfur-rich iron mine environment that appear to be mediating the deposit of microcrystalline jarosite (Fig. 2), and organisms that utilize copper sulphides produc-ing copper oxides and sulfates as byproducts of that transformation (Fig. 3).

The association of sulfate minerals with microbial communities can be seen in the physical proximity of organism with mineral grains, and in the gradual trans-formation from amorphous to crystalline phases in the living materials. No such transformations occur in killed controls. Such microbial communities are of relevance to potential biology and mineralogy of Mars.

Methods: We analyze isotopic signatures of C, S, O, and H/D in both mineral and biological compo-nents. We assess other geochemical biosignatures and bulk chemistry. To study the association of various elements with organisms, we construct elemental maps via electron microprobe of C, S, and other relevant elements. Organisms that are growable are maintained in culture and subjected to an array of experiments including those aimed at inducing the same or similar precipitation of minerals that we see in nature. Lastly, we analyze the DNA of both environmental and cul-tured samples to determine organism identities, or their closest relatives if they are unknown strains.

Conclusion: Numerous microorganisms are in-volved in processes that either degrade or precipitate sulfates. The biology of these communites can serve as a comparison model for similar Martian minerals and environments.

References: [1] Boston, P.J. et al. (2006) GSA Sp. Pap. 404,

331-344.

Figure 1: Gypsum paste soaked with sulfuric acid in Cueva de Villa Luz, an active sulfuric acid cave in Tabasco, Mex-ico. White dots on dark material are microbial colonies growing at pH 1.-2.5. Image courtesy of Kenneth Ingham.

Figure 2: Jarosite and microbial filaments and cell bodies mound up in briny samples from the Soudan Iron Mine in northern Minnesota. SEM by Spilde and Boston.

Figure 3: Cellular “bushes” coated with copper oxides de-rived from copper sulfides. SEM by Spilde and Boston.


USE OF THE THERMAL AND EVOLVED-GAS ANALYZER (TEGA) ON THE PHOENIX LANDER TO DETECT SULFATES ON MARS. W.V. Boynton1 and D.W. Ming2, 1Department of Planetary Sciences, Univer-sity of Arizona, Tucson AZ 85721 ([email protected]), 2ARES, NASA Johnson Space Center, Houston TX 77058 ([email protected])

Introduction: TEGA is one of several instruments

on the Phoenix Lander. This lander will launch in Au-gust of 2007 and land in the north polar region of Mars. TEGA is similar to the instrument that originally was provided for the Mars Polar Lander mission of 1999, which failed during descent It consists of eight small ovens, each of which can hold a 0.030 ml sample of Mars regolith. The samples will be delivered to the instrument via a robotic arm that digs or grinds the sample from the martian surface. The samples are heated at a programmed ramp rate (typically 5 to 20 K/min) up to 1000° C. As the sample is being heated, the required heat input is monitored to provide calo-rimeteric data on any phase transitions (This is the thermal analyzer). In addition, the evolved gases that are generated during the heating are analyzed with the evolved-gas analyzer (a magnetic sector mass spec-trometer) to determine the composition of the gases released as a function of temperature.

Expected Results: Iron, Ca, and Mg sulfates have distinct thermal and evolved gas behaviors. We show here the thermal and evolved gas analysis (TA/EGA) using a laboratory based instrument for three candidate Martian sulfates. Ca-sulfates, such as gypsum, do not evolve SO2 in the operational temperature range of TEGA. Gypsum may be identified by a very distinct evolution (endoenthalpic transition) of H2O with an onset of around 100-120°C under the operation condi-tions of TEGA. TA/EGA for the jarositic tephra indi-cates a strong endoenthalpic transition near 420°C, which marks the dehydroxylation of the ferric-OH bonds in jarosite and the evolution of water (e.g., 2KFe3(SO4)2(OH)6 K2SO4

. Fe2(SO4)3 + 2Fe2O3 + 6H2O). A second endoenthalpic transition near 580°C represents the breakdown of sulfate in jarosite. During this transformation, K2SO4 (and Na2SO4) and Fe2O3 form as SO2 is evolved (e.g., K2SO4 . Fe2(SO4)3 K2SO4 + Fe2O3 + 3SO2 + 3/2O2). Mg sulfates have a variety of hydration states that can be characterized by TA/EGA. Kieserite (MgSO4

.H2O) has been suggested as being stable at the surface of Mars [1] and has a similar TA/EGA as jarosite. We are currently charac-terizing the thermal and evolved gas behaviors for a variety of sulfates under conditions that TEGA will operate on Mars such that we will be able to differenti-ate between the sulfates, particularly kieserite from jarosite and other Fe sulfates.

References: [1] Vaniman et al., Nature. Vol. 431, 2004.


REMOTE SENSING OF WESTERN AUSTRALIAN SULFATE DEPOSITS AND APPLICATIONS FOR MARS. A. J. Brown1, 1SETI Institute, 515 N. Whisman Rd, Mountain View, CA 94043, http://abrown.seti.org

Introduction: The European hyperspectral imag-

ing instrument Observatoire pour la Minéralogie, l'Eau, la Glace et l'Activité (OMEGA) has been in operation around Mars since early 2004. OMEGA has constructed imaging maps covering almost the entire Martian surface. OMEGA has returned evidence of surficial sulfate deposits at several locations around the Martian globe [1].The presence of sulfates on the Mar-tian surface has important links with past water and possible life on Mars.

Figure 1 – Gypsum abundance mapped using ASTER false color R4(1.65) B5 (2.16) G6 (2.2) image showing sulfates in red.

On Earth, sulfates most commonly form in dry lake evaporite basins, many examples of this type of de-posit are in evidence in arid Western Australia. A number of these dry lakes criss-cross the ancient (late Archean) Yilgarn Craton. The ultramafic-mafic vol-canic flows in this region make the Yilgarn a good analog for the volcanic flood basalts of Mars.

In 2004, a hyperspectral imaging survey of the Yil-garn Craton was carried out using the airborne HyMap instrument. We have analysed this hyperspectral coverage of the evaporite deposits of the Yilgarn GGT and found large deposits of gypsum in evidence. We intend to use an analysis method based on curve fitting of individual spectra in the dataset, to compare the results for the Martian North Polar region with the arid Western Australian evaporite deposits [2].

Hyperspectral Dataset: The airborne dataset was collected by the CSIRO Division of Exploration and Mining in 2004 as part of a field mapping for the Next Generation Maps project [3]. The data was obtained using the Australian built HyMap hyperspectral spec-trometer, operated by HyVista Corporation (www.hyvista.com). HyMap is a VNIR (0.4-2.5 mi-cron) spectrometer, and was configured to obtain spec-tels 5m a side on the ground. This dataset has been complemented by ASTER imagery of the region (Fig-ure 1).

Results: Using standard multispectral analysis techniques, mineral maps have been obtained of gyp-sum abundance in the dry lakes near Kalgoorlie (Fig-ure 1). These show the central regions of dry lakes to be high in gypsum abundance – as measured by the depths of their absorption bands. In the future, the hy-perspectral dataset will be analyzed completely using the absorption band modeling technique in order to measure such parameters as wavelength center, ab-sorption band width and asymmetry.

Fieldwork: Colleagues working on the airborne hyperspectral survey collected several samples of gyp-sum near Kalgoorlie. We have collected a wide range of library spectra from the literature covering the Ca

and Mg sulfates that we wish to study. These spectra currently form the basis of discriminating these mate-rials in the field (and on Mars). It is our intention to further refine the locations of the absorption bands of these spectra so that the cause for each band can be well understood, and also attempt to find additional diagnostic absorption bands for other minerals in an acid sulfate weathering environment. This work has recently been funded [4]. It is critical we identify what the most likely minerals (down to the specific species of sulfate) are in a basaltic acid weathered region and what the implications are for detecting these minerals from airborne and satellite survey.

Future work: This project has started to collect the necessary data for identifying sulfates and deter-mining hydration state and cation type using hyper-spectral data. Future work is intended to use an absorp-tion band modeling approach to interpret reflectance spectra of sulfates with variable cation and hydration state. The results will be a guide to the features in IR spectra that are indicative of cation type and hydration state, linking molecular cause to spectral effect.

Conclusion: Understanding of sulfate distribution, species and hydration state in the Martian regolith will lead to greater understanding of the Martian hydro-logical cycle. In the forthcoming year, with the addi-tion of CRISM data, sites where sulfates have been discovered will be analyzed with absorption band modeling techniques and the knowledge gained by this project will be used to attempt to determine sulfate hydration states and distributions all over the Red Planet.

References: [1] Bibring, J.-P. et al., (2006) Sci-ence, 312 400-404. [2] Bishop, J.L. (2006) this work-shop. [3] Brown, A. J. and Cudahy, T. J. (2006) SPIE Electronic Imaging, San Jose, 16-20 Jan 2006 [4] Crowley, J. K. et al., (2006) this workshop.


http://www.hyvista.com/

SULFUR ON THE MARTIAN SURFACE: IN-SITU DATA FROM ALL LANDING SITES. J. Brückner1 and APXS Team2, 1Max-Planck-Institut für Chemie, J. J. Becher Weg 27, D-55128 Mainz, Germany, [email protected], 2NASA Mars Exploration Rovers Mission.

Introduction: On all landing sites high concen-

trations of sulfur in soils and rocks were determined by instruments onboard the landers Viking 1 and 2, Mars Pathfinder Rover Sojourner, Mars Exploration Rovers Spirit and Opportunity. Measurements were carried out by X-Ray Fluorescence Spectrometers on the Viking landers or Alpha Particle X-Ray Spectrometers (APXS) onboard of all three rovers.

Viking Sites: The surface sampler could not catch any rock piece at either Chryse or Utopia Planitia. However, several soil samples (surface fines or pro-tected fines) could be analyzed. In spite the fact that both landing sites were more than 6000 kilometers apart, the soil compositions were very similar; S con-tents varied between 3.2 weight-percent at Utopia and 2.6 wt.% at Chryse [1]. Soils were characterized to contain mafic material; however, high S (and Cl) con-tents could result from volcanic exhalations [2]. As further landing sites revealed, the soil compositions were very similar suggesting a global homogenization mechanism, such as large dust storms.

Mars Pathfinder Site: In Ares Vallis, soil sites several meters apart were measured by the APXS. The mean S content was 2.7 ±0.3 wt.% (standard devia-tion), which is comparable to both Viking sites [3]. A cemented soil did not show any different concentra-tions for S and Cl. Again the mafic nature of the soils could be confirmed. For the first time, several rocks on the martian surface were measured and a soil-free rock composition could be derived [4]. Since sulfur was used as a tracer for the amount of adhering soil, no intrinsic S contents of the rocks could be obtained [3]. Nevertheless, the Pathfinder rocks seemed to have S contents compatible with those of martian meteorites. In particular, basaltic Shergottites show a mean S con-tent of 0.21 ±0.08 wt.% [5]. This level of S contents could be indigenous to most martian basaltic rocks.

Gusev Crater sites: The soils encountered at the Plains have a rather similar composition with a few exceptions. The mean S contents of the top soil layer (APXS radiation penetrates about 10 µm) is 2.59 ±0.33 wt.% [6]. Three so-called undisturbed soils were discovered that had S contents below 2 wt.%. The rover wheels did scuff a few soils, so-called disturbed soils, whose mean S content is 2.21 ±0.43 wt.%. In the Columbia Hills, three disturbed soils were discovered that had S contents between 13 and 14 wt.% [6]. Here, the soils were enriched with sulfur-bearing compounds probably due to aqueous processes. Trenches, which

were dug by the Rover Spirit, disclosed varying S con-tents ranging from normal soil contents to enrichments of up to 5.6 wt.% [6]. At the Plains, primitive basaltic rocks were encountered that had a mean S content of 0.53 ±0.05 wt.% (abraded surface) somewhat higher than the Shergottites. In the Columbia Hills, several new rock classes were discovered, floats and outcrops; all showing strong indications of alteration. S concen-trations of up to 5.2 wt.% were found [6]. Gusev crater revealed that within several kilometers the chemical composition can vary distinctively, probably depend-ing on their geological history. The Hills, which seem to be older than the Plains, had seen aqueous activities in the past, while the Plains represent the dryer more recent (2 to 3 billion years) environment. Independent of the location, abraded rocks contained at least 0.5 wt.% sulfur, which makes an indigenous S content of the Pathfinder rocks very likely. The assumption of at least 0.3 wt.% S seems therefore to be justified.

Meridiani Planum Sites: The soils at Meridiani Planum vary somewhat in composition depending on how many spherules, which contain high contents of hematite (Fe2O3), are covering the soils. Spherule-free top-most soils have a mean S content of 2.23 ±0.46 wt.% [7,8] and the spherule-covered soils have a simi-lar mean of 2.1 ±0.2 wt.%. However, spherule-rich soils show a mean Fe content of 23.0 ±1.7 wt.% (which causes dilution of other major elements) com-pared to 14.0 ±0.7 wt.% of spherule-free soils [7,8]. All rocks occur as outcrops (except some unusual rocks). Just the abraded rocks have very high sulfur concentrations: mean of 9.1 ±1.1 wt.% with a maxi-mum of 11.5 wt.% [7,8]. These sulfur-rich outcrops occur along a traverse of at least 8 kilometers, where they typically seem to be covered by the ubiquitous soil except for certain locations. The formation of these outcrops could be explained by a mixture of siliciclastic material with brines containing high amounts of salts [7]. Sulfur, a very mobile element, influenced geological processes everywhere on Mars.

References: [1] Banin et al. (1992), Mars, Univ. Arizona Press, 594-625. [2] Baird and Clark (1981), Icarus, 45, 113-123. [3] Brückner et al. (2003), JGR, 108, 8094. [4] Wänke et al. (2001), Space Sci. Rev., 91, 317-330. [5] Meyer (2006), Mars Meteorite Compendium, URL www-curator.jsc.nasa.gov. [6] Gellert et al. (2006), JGR, 111, E02S05. [7] Rieder et al. (224), Science, 306, 1746-1749. [8] Gellert et al., JGR, to be published.


ATMOSPHERIC CONDITIONS ON EARLY MARS AND THE MISSING LAYERED CARBONATES. M. A. Bullock1 and J. M. Moore2, 1Southwest Research Institute, Department of Space Studies, 1050 Walnut St, Suite 400, Boulder, CO 80302; [email protected], 2NASA Ames Research Center, [email protected].

Introduction: Massive layered sediments investi-

gated by the Opportunity rover at Meridiani Planum leave little doubt that liquid water has chemically al-tered the surface of Mars [1]. Stacks of mixed sulfate-siliciclastic layers, 7 m of which are exposed near the rim of Endurance crater, most likely were laid down in a lacustrine environment as evaporitic sediments [2]. MOC and Themis images show that the exposed out-crops at Meridiani are merely a portion of light-toned sediments that are up to 800 m thick and several hun-dred thousand km2 in extent [3]. The OMEGA in-strument on board the Mars Express spacecraft has identified at least some of these layers as evaporitic salts [4].

Aqueous Geochemical Model: We present a sim-ple aqueous chemical model of the formation of the Meridiani sediments, and offer an explanation for why extensive layered carbonates are not found there or elsewhere on Mars [5].

In order to gain insight into how early martian wa-ters could have formed the chemical sediments found at Meridiani, we consider a simplified geochemical system. A body of water is in equilibrium with carbon dioxide at the top and carbonates and sulfates at the bottom. Sulfur is added at the top in the form of sulfu-ric acid. Carbon dioxide partial pressure and sulfuric acid concentration define the stability fields for car-bonate and sulfate.

Based on what was measured by APXS, mini-TES, and the Mossbauer spectrometer on the Opportunity rover at Endurance and Eagle craters, the two most prominent sulfate cations are Mg2+ and Ca2+. [6] We assume that the water was in contact with CO2 at a partial pressure between 0.1 and 3000 mbar and there-fore H2CO3, H2CO3

- and CO32+ were also in the water.

Since we are investigating the precipitation of CO3

2+and SO42- this will happen with the available

cations, mostly Mg2+ and Ca2+. Thus, the initial model system consists of water in

equilibrium with CO2 of some amount, and also Mg2+, Ca2+, CO3

2-, and SO42-. This is equivalently a system

with water in equilibrium with CO2 (at some pressure), CaCO3, MgCO3, CaSO4, and MgSO4.

The chemical system is defined by the reactions: 2 2

3 3CaCO Ca CO+ −⇒ + 2 2

3 3MgCO Mg CO+ −⇒ + 2 2

4 4CaSO Ca SO+ −⇒ + 2 2

4 4MgSO Mg SO+ −⇒ +

2 2 2 3CO H O H CO+ ⇒

2 3 3H CO H HCO+ −⇒ + 2

3 3HCO H CO− + −⇒ +

2 4 4H SO H HSO+ −⇒ + 2

4 4HSO H SO− + −⇒ +

2H O H OH+ −⇒ +

Acid Rain: During the late Noachian, widespread volcanism, such as that associated with the formation of Tharsis [7], very likely injected large amounts of SO2 into the atmosphere of Mars. Efficient photo-chemical conversion of SO2 to H2SO4 [8] would have caused widespread atmospheric precipitation and the acidification of standing bodies of water. Based on the total amount of igneous activity during the Noachian [7], and on estimates of the S composition of Mars magmas [8], there should be enough sulfate to cover Mars in a global layer 100 m thick. Much of this may be in the fines, but massive layered deposits also exist in areas other than Meridiani.

Conclusions: The results of our simple model show that acidic waters in equilibrium with a more massive CO2 atmosphere would precipitate Mg and Ca sulfates but not carbonates. Mars may have sustained a thick CO2 atmosphere, and thus supported liquid water, as long as atmospheric CO2 was precluded from forming carbonates by constantly resupplying volcanic gases such as SO2 to the atmosphere. The dissolved acidic gases would rapidly combine with altered basal-tic minerals to form layered water-lain deposits such as those seen at Meridiani. Once acidic gas production dropped and the waters become pH-neutral, the CO2 atmosphere collapsed to form non-massive, non-layered, poorly consolidated carbonate patinas. Among other things, such patinas were probably sus-ceptible to being transformed into Martian atmospheric dust, further diminishing their detectability.

This work was supported by NASA's Planetary Geology and Geophysics Program.

References: [1] Squyres S. W. et al. (2004) Sci-ence, 306, 1709–1714. [2] Grotzinger J. P. et al. (2005) Earth Planet. Sci. Lett., 240, 11-72. [3] Hynek B. M. (2004) Nature, 431, 156-159. [4] Gendrin A. et al. (2005) Science, 307, 1587-1591. [5] Moore, J.M. (2004) Nature, 428, 711-712. [6] Clark et al. (2005) Earth Planet. Sci. Lett., 240, 73-94. [7] Phillips R.J. et al. (2001) Science, 291, 2587-2591. [8] Settle M. (1979) J. Geophys. Res., 84, 8343-8354.


200 μm200 μm

THE ROLE OF FLUID CHEMISTRY AND CRYSTALLIZATION KINETICS IN Na AND K ZONING IN JAROSITE. P.V. Burger, J.J. Papike, C.K. Shearer and J.M. Karner. Astromaterials Institute, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131.

As jarosite is known to be a prominent phase on

the martian surface, zoning in jarosite crystals likely contains important information about martian surface conditions at the time of deposition [1,2,3]. Here we document several striking examples of Na-K zoning in a suite of terrestrial samples in order to place constraints on the conditions of jarosite growth. The study was carried out using a combination of electron microprobe (EMP), back-scattered imaging (BSE) and energy-dispersive (EDS) mapping techniques.

BSE imaging of a suite of 14 jarosite samples from various terrestrial environments (both supergene and hydrothermal) reveal a range in zoning development, from samples with no zoning to those with spectacular oscillatory bands (Fig. 1,2,3). Differences in zoning among samples is likely due to both crystallization kinetics and fluid chemistry. In these samples, jarosite growth begins with multiple nucleation sites, leading to the growth of numerous euhedral crystals (Fig. 1), possibly when an oxidant is introduced into the system [2,3]. EDS maps and microprobe analyses confirm that these bands are defined by fluctuations in Na and K, while Al and Fe show no variation. Na-K zoning is likely caused by changes in Na and K concentration in the fluid immediately adjacent to zones of crystal growth. In the case of sample AA01AZ (Fig. 1,2), later precipitation/crystal growth is characterized by a higher concentration of Na and lower concentration of K, suggesting the overall fluid composition has become more sodic. Further growth likely results in the coalescing of various crystals, as voids are filled in. Sample GH01UT (Fig. 3) may represent this later stage of crystal growth; while it would appear that there were once numerous crystals, one large grain has developed, and subsequent crystal growth is characterized by zoning along the periphery of the large grain, the area to which fluids were likely sequestered once voids between crystals had been filled in. While zoning is quite dramatic, electron microprobe analyses [4] suggest that the overall Na/(Na+K) of these two samples are quite low when compared to the samples discussed in [3], and zones are the result of changes in fluid Na and K concentration in a very limited Eh/pH range. REFERENCES. [1] Klingelhofer et al. (2004) Science, 306, 1740. [2] Papike et al. (2006) GCA, 70, 1309. [3] Papike et al. (2006) AmMin, 91, 1197. [4] Papike et al. (this volume).

Figure 1. Jarosite crystals with prominent oscillatory zoning in sample AA01AZ. Darker regions are more sodic.

Figure 2. False-color BSE image of a jarosite crystal in sample AA01AZ. Cooler regions are more sodic.

Figure 3. False-color BSE image of jarosite in sample GH01UT.

50 μm50 μm

100 μm100 μm


INTRINSIC ACIDITY OF JAROSITE AND OTHER FERRIC SULFATES AS AN INDICATOR OF HOW THEY FORM. D. M. Burt1 1School of Earth and Space Exploration, Arizona State University, Box 871404, Tempe, AZ 85287-1404 ([email protected]).

Introduction: The sulfate-rich (or at least S-rich)

nature of the martian surface was indicated by analyses performed by the Viking landers, and was attributed to some sort of planet-wide volcanogenic “acid mist” process [e.g., 1]. More recently, acid sulfates (jarosite group) were indicated by the Mossbauer spectrometer on the Mars Exploration Rover Opportunity at Merid-iani Planum [2], and were attributed initially to deposi-tion by evaporating acid seas or lakes [3], and later, to deposition by rising sulfuric acid groundwaters [4]. All of the hydroxyls in the jarosite formula, as normally written, apparently were taken to indicate that it must have formed in an extremely water-rich environment (i.e., under water). Another hypothesis for sulfate for-mation at Meridiani involved hot acid steam in a giant solfatera system [5]. Independently, the Spirit rover discovered isolated areas of extreme subsurface en-richment in ferric sulfate salts at Gusev Crater [6]. Most recently, OMEGA remote sensing data indicated abundant sulfates in layered rocks and fines in many areas of Mars [7]; sulfate formation was attributed to a volcanic acid mist episode that postdated the “warm wet” formation of surficial clays in the most heavily cratered areas. As a suitability test for Mars, do any of these conflicting hypotheses reflect how jarosite and other ferric sulfates typically form on Earth? No!

Jarosite as Acid: If the K-jarosite formula is dou-bled to K2Fe3+

6(SO4)4(OH)12, it would appear to con-tain 12 hydroxyls, in support of an “abundant water” hypothesis. However, this formula can alternatively be written as 6FeO(OH) + K2SO4 + 3H2SO4. In other words, it can be written as as a combination of goethite (or hematite + H2O) with ¼ neutral salt (arcanite) and ¾ sulfuric acid. Jarosite can thus be considered a crys-talline form of sulfuric acid (analogous to crystalline sodium bisulfate that is added to plumbing fixtures to remove hard water deposits). The jarosite end-member hydronium jarosite, with H3O+ in place of K+, is en-tirely ferric oxide plus acid. Contrary to what has been claimed for Meridiani, such jarosite-group minerals don’t form in the presence of abundant liquid water (except fairly concentrated sulfuric acid), and, in fact, are stable in the presence of very little water [8], as on the present martian surface (or on an Arizona mine dump in June).

Other Ferric Sulfates as Acids: Jarosite (hy-dronium jarosite) is only one of many iron sulfates. Others (neglecting ferrous phases and polymorphs) include mikasaite, lausenite, kornelite, coquimbite,

quenstedtite, butlerite, fibroferrite, amarantite, hoh-mannite, rhomboclase, ferricopiapite, and schwert-mannite. All can be considered as a combination of ferric oxide, water, and sulfuric acid (i.e., as crystalline forms of sulfuric acid). Of these, the most acid is pos-sibly rhomboclase, HFe3+(SO4)2

.4H2O, sometimes seen on mine waste as a blue efflorescence. Owing to com-positional degeneracies, one can write ferricopiapite (bright yellow) + H2SO4 ==> coquimbite (gray) + H2SO4 ==> rhomboclase (blue). In other words, these three colored minerals are potential indicators (or buff-ers) of sulfuric acid activity. They can occur together as layered efflorescent crusts, with the “more acid” (gray or blue) phase on top. A process of “damp” (but not overly wet) sulfide weathering is how such ferric sulfates typically form in terrestrial mine waste [e.g., 9], and could well be how they formed on Mars [10,11], perhaps after the surface had become too dry and cold to form abundant clays [7]. This hypothesis (minus the impact mining part) originated with Roger Burns [11,12]. No life-hostile, sulfuric acid atmos-phere or hydrosphere (or steam) is indicated or re-quired. Just moisture, dispersed sulfides, and an oxi-dizing environment.

Summary: Jarosite and other ferric sulfates typi-cally form as coatings and efflorescences on and in mine waste, via moist weathering of contained iron sulfides. They can be thought of as ephemeral crystal-line forms of sulfuric acid. Add too much water (as when it rains), and they dissolve incongruently, acidi-fying the water and leaving ferric oxide (goethite or hematite) behind. The originally sulfidic surface of Mars may not have experienced rain for about 4 billion years, if ever, accounting for the preservation of acid sulfates there.

References: [1] Settle M. (1979) JGR, 84, 8343–8354. [2] Klingelhofer G. et al. (2004) Science, 306, 1740-1745 [3] Squyres S. W. et al., Science, 306, 1698-1703. [4] Squyres S. W. and Knoll A. H. (2005) EPSL, 240, 1-10. [5] McCollom T. M. and Hynek, B. M. (2005) Nature, 438, 1129-1131. [6] Wang A. et al. (2006) JGR, 111, doi:10.1029/2005JE002513. [7] Bi-bring J.-P. et al. (2006) Science, 312, 400-404. [8] Navrotsky A. et al. (2005) Icarus, 176, 250-253. [9] Jerz J. K. and Rimstidt J. D. (2003) Am. Min., 88, 1919-1932. [10] Knauth L. P. et al. (2005) Nature 438, 1123-1128. [11] Burt D. M. et al. (2006) This Confer-ence (submitted). [12] Burns R. G. (1988) Proc. LPSC, 18th, 713-721.


mailto:[email protected]

IMPACT EXCAVATION OF SULFIDES THAT THEN WEATHER INTO SULFATES: AN ASTROBIOLOGY-FRIENDLY EXPLANATION FOR ACID SULFATE FORMATION ON MARS. D. M. Burt1, L. P Knauth1 and K. H. Wohletz2, 1School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 ([email protected]; [email protected] ), 2Earth and Environmental Sciences, Los Alamos National Lab, Los Alamos, NM 87545-1663 ([email protected] ).

Introduction: Based on recent orbital and all lan-

der/rover observations to date, much of the surface of Mars appears to be highly enriched in sulfate minerals; much also is heavily cratered. We suggest that these two observations can be correlated, especially as re-gards the origin of the acid sulfate-rich, cross-bedded sediments discovered by the Opportunity Rover in Meridiani Planum [1], and local Fe-sulfate enrich-ments discovered by the Spirit Rover in Gusev Crater. Our impact excavation hypothesis [1] represents a modification (updated for cratering) of the gossan hy-pothesis of the late Prof. Roger Burns of MIT.

Gossan Hypothesis: Burns [2-6] hypothesized that the surface mineralogy and color of Mars could, at least in part, be caused by the weathering of sulfide minerals in martian igneous rocks. Based on the obser-vation that martian mafic rocks appear to be at least twice as rich in Fe as terrestrial equivalents, he con-cluded that they should also be richer in reduced S and in cumulate Fe,Ni-sulfides (dense immiscible droplets that “rain out” of the liquid magma). Weathering of sulfide deposits on Earth typically produces Mars-colored, acid-sulfate bearing deposits called gossans (rusty areas long sought by metal prospectors). Burns simply proposed the same process of gossan formation could have occurred on Mars. In his multiple discus-sions of Mars gossans and weathering, Burns never mentioned impact cratering and its associated com-minution (rock breakage) and sulfide dispersal.

Open-Pit Mines as Mars Analogs: Rather than gossans as Mars analogs, we suggest Arizona-style open-pit sulfide mines as better analogs for acid sulfate formation during weathering. Open-pit sulfide mines are analogous to large impact craters that intersected subsurface magmatic sulfide deposits (common on Mars, according to Burns [2-6]). Surrounding rock-strewn mine dumps are then analogous to impact-excavated breccias. Finally, associated sandy, layered, mill tailings (the result of fine comminution during ore separation in a milling operation) are analogous to distal sandy layered impact surge and fall deposits. In contrast to their apparent absence on the Moon, such non-ballistic layered deposits are presumed to be wide-spread on Mars [1] owing to its atmosphere and sub-surface volatiles. In this regard, we note that sulfide minerals, compared to silicates, tend to be soft and extremely brittle, greatly facilitating shattering and

dispersal during impacting, and greatly speeding up weathering afterwards. We further note that many sul-fate minerals are extremely hygroscopic (able to ex-tract moisture even from dry air), so that subsurface moisture should be readily available to promote sulfide weathering, once the process has begun (i.e., owing to positive feedback, it should go to completion).

Discussion: This explanation for the formation of jarosite and other acid sulfates on Mars (impact exca-vation of sulfides, followed by their in situ oxidation to acid sulfates) provides a simple alternative to far more complex hypotheses involving planet-wide, volcani-cally-derived sulfuric acid mists, sulfuric acid lakes and streams, or sulfuric acid groundwaters, such as have been proposed by other authors [e.g., 7,8,9]. These hypotheses suffer numerous contradictions, not the least of which is the fact that acids in contact with brecciated mafic rocks should be neutralized almost immediately, with formation of abundant clays. By our alternative impact hypothesis, the surface of early “warm, wet” Mars dried up and froze down while im-pacting still continued. Impacts into a partly frozen, salty/briny, locally sulfide-rich regolith, followed by moist weathering, produced all of the sedimentary and geochemical feathers seen at Meridiani Planum and probably in many other layered deposits on Mars [1]. Martian breccias and layered sediments are then analo-gous to weathered sulfide mine wastes, but with the mining and milling having been done by impacts. Planet-wide sulfuric acid mists and liquids are not par-ticularly friendly to life [10]. In contrast, sulfide weathering in terrestrial mine waste is commonly ac-companied by intense microbial activity. Did such activity accompany sulfide oxidation on Mars? If so, acid sulfate-bearing areas might provide good targets for future astrobiologic investigations.

References: [1] Knauth L. P. et al. (2005) Nature 438, 1123-1128. [2] Burns R. G. (1986) Nature 320, 55-56. [3] Burns R. G. (1987) JGR, 92, E570–E574. [4] Burns R. G. (1988) Proc. LPSC, 18th, 713-721. [5] Burns R. G. and Fisher D. S. (1990) JGR, 95, 14,169–14,173. [6] Burns R. G. and Fisher D. S. (1990) JGR, 95, 14,415–14,421. [7] Squyres S. W. et al. (2004) Science, 306, 1698-1703. [8] Squyres S. W. and Knoll A. H. (2005) EPSL, 240, 1-10. [9] Bibring J.-P. et al. (2006) Science, 312, 400-404. [10] Knoll A. H. et al. (2005) EPSL, 240, 179-189.





MAPPING SULFATES IN NEVADA USING REFLECTED, EMITTED, MULTI-SPECTRAL ANDHYPERSPECTRAL SYSTEMS. W. M. Calvin1, R.G. Vaughan2, C. Kratt3, and J. D. Shoffner1, 1Geological Sci-ences, MS172, University of Nevada – Reno, NV 89557, [email protected]; 2Jet Propulsion Lab,[email protected]; 3Desert Research Institute, [email protected].

Overview: The remote sensing group of the Ar-thur Brant Laboratory for Exploration Geophysics atUNR has used a wide variety of airborne and space-borne sensors to map the occurrence of sulfates usingboth reflected solar wavelengths (0.4 to 2.5 µm) andemitted thermal wavelengths (7 to 14 µm). Data setsrange in spatial resolution from 2m/pixel to 30m/pixeland spectral fidelity varies from hyperspectral systems(hundreds of channels) to multi-channel systems. Datasets have been acquired over geothermal systems andold mine districts. New work on an acid producingsystem in an historic California mining district is justbeginning. Here we summarize the results of theseefforts [1-5] and make recommendations for the explo-ration of Mars, based on our terrestrial experience.

Geologic terrains: We have mapped sulfates inNevada in association with current geothermal systemsat Steamboat Springs [1,2], Brady’s Hot Springs [3], inregions of geothermal development potential on Pyra-mid Lake Paiute Tribal Lands [4], over the historicmining district of Virginia City [5], and are beginningto examine Leviathan Mine, CA.

Geothermal Systems. Geothermal systems in Ne-vada are concentrated in regions of extensional tec-tonics, rather than active volcanism as seen in the Pa-cific “ring of fire”. These systems are typified by ac-tive fumaroles and mud pots, large expanses of steam-ing ground, recent and ancient siliceous sinter andstructurally controlled tufa (carbonate), and of course,sulfates. Sulfates tend to concentrate near old ventstructures or around current fumaroles (Fig 1). Yellowand white crusts are common, and iron alteration isalso sometimes seen. At Pyramid Lake sulfates areseen in playa evaporites and in seeps where geothermalground water reaches the surface.

Mining Districts. Historic mining districts in thestate tend to occur in areas of intrusive volcanics withsubstantial hydrothermal alteration with varying levelsof sulfur. Virginia City economic mineralization ap-peared during a low-sulfidation hydrothermal phase,but many sub-economic minerals contain sulfides thatweather in mine tailing piles to form hydrated sulfateminerals. At Leviathan, the region is hosted by intru-sive volcanics with former open pit mining of elemen-tal sulfur – presumably a capped vent.

Sensors and Data Sets: We have used a variety ofairborne hyperspectral systems: AVIRIS, HyMAP,HyperSpecTIR, all measuring the optical and short-wave infrared, and SEBASS, measuring the thermal

infrared. Multi-channel spaceborne data from ASTERand airborne data from MASTER have also been usedto map mineralogy at varying spatial scales. We per-form extensive field validation of remotely mappedmineralogy using portable field spectrometers (ASD,D&P) and collect samples for laboratory measure-ments and XRD corroboration of mineral species.

Mapping Results: We have mapped common sul-fate species at these locations, including alunite, gyp-sum, and jarosite. In many regions hydrated sulfateswere mapped remotely and later XRD characterizedthem as hexahydrite, alunogen, tamarugite, or kie-serite. In all cases the most diagnostic spectral featureswere identified using hyperspectral airborne data athigh spatial resolution corroborated with field meas-urements. Coarse spatial resolution and low spectralfidelity can broadly identify alteration zones, but arenot capable of uniquely identifying specific sulfateminerals. In many instances, mixed sulfates wereidentified in remote data sets, but field and laboratorymeasurements were needed to confirm individual spe-cies. Sulfates are identified in both shortwave andthermal infrared data and using measurements fromboth spectral regions allows greater mineral identifica-tion ability.

Recommendations: Laboratory measurements ofmore exotic sulfate species are needed. Our experi-ence shows that both high spatial and spectral resolu-tion are needed to map these minerals remotely. Spec-tral identifications benefit from complementary XRD.

Figure 1: Vent structure at Brady’s with sulfur/sulfatecrusts and iron alteration.

References: [1] Vaughan R. G. et al. (2003) Re-mote Sensing Env., 85, 48. [2] Vaughan R. G. et al.(2005) Remote Sensing Env., 99, 140. [3] Kratt C. et al.(in press) Remote Sensing Env. [4] Kratt C. et al.(2005) Geothermal Resources Council Trans., 29CDROM. [5]Vaughan R. G. and W. M. Calvin (2005)Geol. Soc. NV Symp. Proc., Vol II, 1035.

Acknowledgements: This work has been sup-ported by PGG, GSRP, EPSCOR, DOE, and MER.


Cracks and Fins as Evidence for Water Evaporation and Condensation Associated with Temperature Changes in Hydrous Sulfate Sands G. V. Chavdarian and D. Y. Sumner, Geology Department, University of California-Davis, Davis, CA 95616, [email protected], [email protected]

Introduction: The Mars Exploration Rover Op-

portunity, on Meridiani Planum, is documenting sul-fate-rich sedimentary rocks that formed in eolian envi-ronments with some evidence for overland water flow [1], [2]. Contractional cracks on outcrop surfaces de-fine centimeter to decimeter scale polygons that cross-cut bedding in Endurance Crater and on the plains of Meridiani. The perpendicular-to-outcrop surface orien-tation of the cracks is inconsistent with synsedimentary contraction [3]. Some cracks in Endurance Crater are associated with fins, which are mm-thick, platy fea-tures that protrude a few centimeters above outcrops. Fin geometry is consistent with differential cementa-tion along cracks, followed by differential weathering. Frost observed on Opportunity demonstrates modern atmospheric water cycling. We use observations from an analog site at White Sands National Monument, New Mexico, to provide insights into processes form-ing cracks and fins.

Cracks and Fins in Gypsum Sand: Dunes and playas at White Sands National Monument provide excellent analogs for sedimentary structures in Merid-iani outcrops because of the ubiquitous hydrous sulfate (gypsum) sand and the similarity of depositional envi-ronments. Fieldwork at White Sands has demonstrated that cracks and fins form seasonally in the gypsum sand [4]. Unfilled polygonal cracks were actively forming in January 2005 in the moist and cohesive sand (Figure 1A); the moisture was due to frost. At all other times, including in dry January 2006, cracks on dune slopes were covered and dry, and not actively forming. However, cracks did form after one signifi-cant rainstorm in June 2005. Cracks on dune slopes crosscut bedding as do Meridiani cracks.

Figure 1: A: Cracks on a dune slope in gypsum sand in January 2005 at White Sands National Monument. B: Tan fins along a crack edge that stand up to a cen-timeter above the surface.

Fins are also present at White Sands [4]. Slightly

cemented tan colored fins were only present in January 2005 when abundant frost was present (Figure 2B).

Tan fins are thin, platy, preferentially cemented fea-tures that protrude a few centimeters out of the dune sand along crack edges. Tan fin surfaces always face into the wind and are composed of finer grains than the surrounding sediment.

Results: Temperature and humidity loggers moni-toring subsurface conditions at 10 minute intervals since January 2006 show that the air between sand grains retains 100% humidity with daily temperature fluctuations. Temperature varies with depth; at the surface, daily fluctuations are up to 30°C, whereas at 45 cm daily fluctuations are ~1ºC. The constant hu-midity with temperature changes requires water to evaporate and condense on a daily cycle, possibly in-ducing precipitation of sulfate cements. Summer tem-perature changes may also promote cementation as the sand grains skirt across the gypsum-anhydrite transi-tion range of 42-60ºC depending on water activity [5]. Cracks may form as the grains contract during dehy-dration. Hydrous Mg-sulfates break down into water plus less hydrous Mg-sulfates at temperatures near 0ºC [6]. Therefore, a similar volume-loss process may produce cracks on Meridiani when surface sediment temperatures cycle above and below 0°C. Thus, at-mospheric water cycling with the evaporation (or sub-limation) and condensation of water associated with hydrous sulfates may promote crack formation in sul-fate sand both at White Sands and on Mars, implying an active water vapor cycle on Mars in recent history.

Field observations of variable cementation along crack edges and adhesion structures suggest that tan fins at White Sands form from 1) preferential cementa-tion along cracks and 2) adhesion of fine-grained parti-cles to structures above the sediment surface. Near-surface water cycling may also play a role as tan fins were only present when there was abundant frost. Laboratory experiments are currently underway to un-derstand crack and fin formation. These or similar processes may provide a testable model for crack and fin formation in Meridiani Planum outcrops

References: [1] Grotzinger J. P. et al (2005) EPSL, 240, 11-72.

[2] Squyres S. W. and Knoll A. H. (2005) EPSL, 240, 1-10. [3] McLennan S. M. et al (2005) EPSL, 240, 95-121. [4] Chavdarian G. V. and Sumner D. Y. (2006) Geology, 34, 229-232. [5] Freyer D. and Voigt W. (2003) Monatshefte für Chemie, 134, 693-719. [6] Hogenboom D. L. et al (1995) Icarus, 115, 258-277.

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Figure 1: TGA Results

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WATER CONTENT AND DEHYDRATION BEHAVIOR OF Mg-SULFATE HYDRATES. S. J. Chipera, D. T. Vaniman, and J. W. Carey, Earth and Environmental Sciences, Los Alamos National Laboratory, MS D469, Los Alamos, NM 87545 ([email protected])

Introduction: Recent studies have been under-

taken to characterize stability relationships between the various MgSO4 hydrates [1,2,3]. These studies have found, however, that the MgSO4 hydrate system is extremely complicated, with numerous unexpected results. In addition to the known 1, 2, 4, 5, 6, and 7 hydrates found in nature, numerous MgSO4 hydrates have been synthesized including several phases in these studies which have not been previously de-scribed. Thermogravimetric analyses were conducted on the various MgSO4 hydrates to characterize water content and thermal evolution in an attempt to gain a better understanding of the relationships between these phases.

Methods: Thermogravimetric analyses (TGA)

were conducted using a DuPont 951 thermogravimet-ric analyzer operated with Omnitherm Corporation hardware and software. Typically, ~15 mg samples were analyzed from ambient temperature to 600°C at 10°C/min, using 50cc/min dry N2 as a purge gas.

Results: TGA is a powerful method that measures

both the amount of water and dehydration behavior in hydrous phases. Figure 1 shows the TGA results for various MgSO4 hydrates plotted as sample weight vs. temperature upon heating. A trend is seen in the data with water release occurring earliest in the most hy-drated phases (e.g, epsomite) and later in the least hy-drated phases (mono-hydrates) where the water is more tightly bound in the crystal structure.

The more hydrous phases (epsomite-7H2O, hexa-hydrite-6H2O, pentahydrite-5H2O, starkeyite-4H2O) have similar dehydration patterns, where water is evolved in a rather continuous fashion with tempera-ture. Epsomite shows an initial weight loss that corre-sponds to loss of the single non-octahedally bound water to form hexahydrite. The intermediate hydrates (2.4-hydrate and sanderite-2H2O) have distinctive weight loss curves with several inflections, which are normally indicative of multiple structural sites contain-ing water. However, available data suggest that these hydrates are reacting to form monohydrates which then dehydrate to anhydrous MgSO4.

Water content in the amorphous phases can be quite variable, with water contents from 2 to 0.6 H2O per MgSO4. Their weight loss patterns resemble those of the hydrated crystalline phases (epsomite, hexahy-drite, starkeyite) that they are made from, even though

they do not retain the crystal structure or water con-tent. The reagent monohydrate and kieserite-1H2O both show gradual weight loss until the single distinct weight-loss event occurring at about 300 to 325°C.

Of interest in the TGA data, water content in the Mg-sulfate system is not always integral (e.g., 2, 3, 4, 5, 6, 7). Also of interest is the final distinct weight-loss event that occurs at approximately 280-300°C in the more hydrated phases. The exact cause for this event is uncertain. Ultra-pure MgSO4 was used to ensure that it was not due to a minor gypsum (CaSO4•2H2O) impurity. The amount of water evolv-ing during this event is also variable as can be seen by comparing the weight-loss patterns of the amorphous phase with the hexahydrite from which it was made. It appears to represent a final terminus of water evolution from either the starting product or from the final dehy-dration of an intermediate reaction product that formed during the heating/dehydration.

References: [1] Chipera, S.J. and Vaniman, D.T,

(2006) Geochimica Cosmochimica Acta, in press. [2] Chou I.-M. and Seal R. R. II (2003) Astrobiology 3, 619-630. [3] Vaniman, D. T. et al. (2004) Nature 431, 663-665.


DIRECT CHEMICAL ANALYSIS ON THE MARTIAN SURFACE: A REVIEW OF SULFUR OCCURRENCE AND INTERPRETATION FROM VIKING TO MER Benton C. Clark, Lockheed Martin, Denver, CO 80201 With five sites on Mars that have been explored in situ, and an equivalent number of orbital mapping missions, Mars emerges as a planet with a sulfate-rich surface, a S-rich mantle, and a probable high S content in its core. Sulfur at the surface of Mars should be in the fully oxidized form because of photochemical oxidants in the atmosphere and in martian soils. Martian meteorites contain ~ 10x higher S than their igneous analogs on Earth. Some rocks on Mars contain even more S , probably due to perfusion by sulfate brines and possibly implying that martian meteorites may be a biased sample of less altered, highly competent launchable rocks. Globally-distributed martian soils contain 4 to 7 wt % SO3, with a nearly uniform molar S:Cl ratio of ~4:1. Soil trends with anionic salt components are indeterminate with respect to cations despite an extensive high-precision data set, consistent with incorporation of volcanic volatiles containing S and Cl. Condensed SOx gases and H2SO4 cannot be ubiquitous on Mars, however, because atmospheric concentrations are well below their equilibrium vapor pressures. MgSO4 enrichments have been detected in some indurated soils (duricrust) and trenches. Thermal cycling of H2O frosts to provide moderate ion mobility may favor formation of weak duricrusts. Non-systematic Br enrichments may result from similar mobilizations. High concentrations of kieserite, polyhydrated MgSO4 and gypsum on the ~10 km scale occur in some regions. Sedimentary outcrops at Meridiani Planum are composed of up to one-half salts, including Mg, Ca and Fe (jarosite) sulfates cementing silicate and Fe oxide grains. A low-pH range of 3 to 5 is indicated for formation and preservation of jarosite. Opposite distributions of MgSO4 and chlorides in outcrop sequences may be explained as solubility in aqueous brines governed by freezing-point depression. CaSO4 enrichments have been detected in two sets of altered rocks in the Columbia Hills of Gusev crater. Whitish powder churned from shallow depths (~ 10 cm) at multiple locations in Columbia Hills is almost pure ferric sulfate with silica and sometimes MgSO4. Low-Fe “Independence class” material may be a source of this Fe. No conclusive detections have been made of Na or Al sulfate salts, in spite of important occurrences in terrestrial settings. Both Na and Al tend to correlate well with Si content, indicating their preservation as primary plagioclase. In spite of the widespread sulfate, there are significant concentrations of olivine in soils and some basalts. Soils are at approximately one-fourth of saturation for SO3 with respect to modeled original olivine and pyroxene. Inferred content of highly soluble MgSO4 in sedimentary outcrop and soils provides a tracer indicating a lack of exposure to significant quantities of meteoric H2O or groundwater since formation of craters at Meridiani or emplacement of soils at other sites. Shallow soluble ferric sulfates in Columbia Hills could indicate emplacement by upward evaporation, but the inferred water table would need to vary greatly in altitude over a relatively short distance. The sulfur cycle on Mars presumably lacks the terrestrial complications of subduction, mid-ocean ridge recirculation, and extensive biological processing. Carbonate deposits on Mars may be generally encrusted with sulfate-rich weathering rinds, rendering their detection much more difficult. Impact cratering is a relatively more important process on Mars, however, providing a mechanism for re-introducing S-gases into the atmosphere.


LASER INDUCED BREAKDOWN SPECTROSCOPY (LIBS) REMOTE DETECTION OF SULFATES ON MARS SCIENCE LABORATORY ROVER. S.M. Clegg1, R.C. Wiens2, M.D. Dyar3, D.T. Vaniman4, J.R. Thompson2, E.C. Sklute3, J.E. Barefield1, and S. Maurice5 1Advanced Diagnostics and Instrumentation Group, Los Alamos National Laboratory, Los Alamos, NM 87545, [email protected], 2Space Sciences and Applications Group, Los Alamos National Laboratory, Los Alamos, NM 87545, 3Earth and Environment Department, Mount Holyoke College, South Hadley, MA 01075, 4Hydrology and Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545, 5Centre d’Etude Spatiale des Rayonnements, Toulouse France.

Introduction: The mineralogy and chemical char-

acteristics of Martian surface sulfate deposits can pro-vide key information about aqueous processes, hydro-geologic cycling, and the history of atmosphere/soil interactions. In this paper, we show that the ChemCam Laser Induced Breakdown Spectrometer selected for the Mars Science Laboratroy (MSL) Rover can re-motely probe and distinguish among various surfur containing minerals. Working with a laboratory LIBS instrument similar to ChemCam, we probed and char-acterized various sulfur-containing minerals including jarosite, pyrite, gypsum and anhydrite. Analysis of the elements in each sample observed with LIBS is used to reconstruct the composition of the sample probed.

Experimental: LIBS involved ablating a small amount of material from the surface of the sample with a focused Nd:YAG laser (20mJ/pulse, <1GW/cm2). The samples were placed 5.4 meters away from the LIBS instrument in a vacuum chamber filled with 7 Torr CO2 to simulate the Martian atmosphere. This produced a plasma containing electronically excited atoms, ions and small molecules that expand from the surface. As these excited species relaxed back to the ground electronic state, they emitted light characteris-tic of the identity of the elements present in the sam-ple. Some of this emission was directed into Ocean Optics HR2000 dispersive spectrometers and detected with a CCD camera. Thompson et al. [1] contains a detailed description of the experimental setup.

Figure 1 is an example of the structurally rich LIBS spectrum obtained from a jarosite-containing rock. The sample, from the Apex Mine in Arizona, has coatings of essentially pure jarosite (mineral identification by X-ray diffraction). The top spectrum depicts the emis-sion from a portion of the visible region in which some of the more prominent peaks are annotated. The bot-tom spectrum covers the region of the visible spectrum in which three emission lines from sulfur are observed.

Results: There are two significant challenges to detecting S with LIBS. First, the strongest S LIBS emission lines are found in the vacuum UV (180.73nm) and in the NIR (>900nm)[2,3]. The ChemCam instrument’s spectral range is 240 – 800nm and consequently, S can only be detected by the weaker emission lines in the 400 – 600nm region.

Secondly, Dudragne et al. [2] demonstrated that elec-tronically excited S readily reacts with oxygen. While the reduced Martian atmosphere produces much stronger LIBS signals, LIBS will still break down the atmospheric CO2 and produce excited oxygen.

Despite these challenges, observations from an in-strument similar to ChemCam were used to character-ize emission from several sulfur-containing minerals. Spectra similar to those in Figure 1 were collected for each sample. Major elemental composition as well as the lighter elements present in functional groups con-taining sulfur and carbon were extracted from each sample. These observations demonstrate ChemCam’s ability to distinguish between various sulfate assem-blages likely to be found on the Martian surface.

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References: [1] Thompson J. R. (2005) JGR-Planets, 111, E05006. [2] Dudragne L. et al. (1998) Appl. Spec., 52, 1321-1327. [3] Salle B. et al. (2004) Spec. Acta B, 59, 1413-1422.


Estimating minimum volumes of water involved in formation of sulfate evaporite deposits. Max Coleman1 and Diana Blaney1, 1Jet Propulsion Laboratory, California Institute of Technology (4800 Oak Grove Drive, Pasadena, CA 91109. [email protected],gov).

Introduction: The description of the Burns For-

mation, Meridiani Planum, as an eolian sulfate evaporite deposit [1] raises the question of how much water was involved in its deposition. Sedimentary ba-sin volumes can give estimates of the maximum water volume previously present [2] but are not appropriate for evaporite basins. The complexity of water volume estimation is exacerbated by: the eolian transport of the sulfate grains from the evaporitic basin and whether it was from a single body of water or if the same water was recycled during evaporation.

We propose a geochemical approach to estimate the minimum volume of water involved in the process by in situ analysis of relatively few evaporite crystals.

Geochemical approach: Crystals grow radially by successive episodes of precipitation forming layers around the nucleus. Analysis of successive growth zones in minerals can reveal the history of changing environmental conditions during crystal growth [3], but has not been applied to monitor changes during evaporation. An isotopic phenomenon allows the op-portunity to interrogate individual grains in which in-ternal composition variations record the history of formation (including amount of water involved) and any possible subsequent alteration. Growth of a min-eral in an aqueous system causes a shift of the relative abundances of stable isotopes (34S/32S and 18O/16O) and an opposite shift in the material remaining in solution.

Mineral compositions of Burns Formation sulfates have not been determined. Although not a likely can-didate we use the example of calcium sulfate (gypsum) crystallization because it is one of the few salts for which the isotopic shift has been measured (+1.65‰) [4]. Changes in isotopic composition follow a form of the Rayleigh fractionation equation: for the reaction,

sulfatesolution sulfatesolid, R/R0 = f( -1), where R = 34S/32S of the solid at any time, R0 = initial value of R, f = the fraction of sulfate left in solution, = Rsolid / Rsolution (the isotopic fractionation factor). In

Fig 1, the values for both solution (lower line) and crystals (upper line) show parallel trends and relatively large and nonlinear changes in isotopic composition, despite the small, initial isotope effect.

Isotopic analysis of successive zones in evaporite mineral crystals, and estimating their relative volumes will determine where in the evolution trend the zones grew, a nonlinear evolution. Thus we can extrapolate back to the initial condition (f=1) and the original mass of gypsum in solution, even if examples of the first-formed crystals are not analyzed or not even preserved. Zonal analysis of a few crystals will show if they are part of the same evaporitic system and together with outcrop data allow estimation of bulk isotopic masses and what fraction of the total evaporation record it represents. Gypsum solubility is relatively independent of temperature, 2.42 – 2.79 g/L between 0° and 50°C [6] and thus the minimum water volume involved can be calculated. Equally, changes in sulfate sources could be identified by step changes in isotopic compo-sition. A further advantage is that sulfur and oxygen in sulfate, even in solution, are resistant to isotopic ex-change and will preserve their original signature [8].

Validation: Data on crystallization of sodium chlo-ride and chlorate samples during the manufacturing process [5] give isotopic trends that conform qualita-tively to the Rayleigh fractionation model. A similar effect has been observed qualitatively on a much larger scale in successive, massive evaporite salt beds [6].

Conclusions: This approach could add valuable in-formation about evaporite deposits. Its use for Mars exploration could be applied to almost any evaporites and would not require sampling from large volumes or over large areas. It would, however, need further cali-bration of isotope effects for potentially relevant min-erals and development of in situ instruments from the current generation of laboratory devices.

References: [1] Grotzinger J. P. et al. (2005) Earth Planet. Sci. Let. 240, 11 –72. [2] Carr M. H. (1996) Water on Mars, O U P, New York. [3] Dickson J. A. D. and Coleman M. L. (1980) Sedimentology 27, 107-118. [4] Thode H. G. et al. (1961) Geochim. Cosmo-chim. Acta 25, 159-174. [5] Ader M. et al. (2001) Ana-lyt. Chem. 73, 4946-4950. [6] Eggenkamp H. G. M. et al. (1995) Geochim. Cosmochim. Acta 59, 5169-5175. [7] Marshall W. L. and Slusher R. (1966) J. Phys. Chem. 70, 4015-4027. [8] Lloyd R. M. (1968) J. Gephys. Res. 73, 6099-6110.

Figure 1. Isotope value changes during crystallization.


Stable isotope characterization of microbially produced sulfate: field data validation at Río Tinto of new laboratory culture experiments. Max L. Coleman1, Stuart Black2, Benjamin Brunner1, Christopher G. Hubbard2, Terry J. McGenity3, Randall. E Mielke1 and Jae-Young Yu4, 1Jet Propulsion Laboratory, California Institute of Technology (4800 Oak Grove Drive, Pasadena, CA 91109, [email protected]), 2School of Human and Environmental Sciences, The University of Reading (Reading RG6 6AB, UK), 3Department of Biological Sciences, University of Essex (Wivenhoe Park, Colchester, Essex, CO4 3SQ, UK), 4Department of Geology, Kangwon Na-tional University (Chuncheon, Kangwon-Do 200-701, Republic of Korea).

Introduction: The sources of sulfate on Mars de-

scribed recently [1-3] have not been determined but one possibility is pyrite oxidation [4]. This exposes another possibility that the oxidation process was mi-crobial. There are many reported stable isotope frac-tionation values associated with microbial oxidation of pyrite for both sulfur [5] and oxygen [6-8]. The oxygen isotope fractionation is large and variable but different results are reported from the various experiments re-ported and explained by differences in experimental conditions [5, 7]. Our experiments on microbial growth of Acidithiobaccillus ferrooxidans oxidizing pyrite have identified isotopic fractionation of sulfur, appar-ent during lag phase of microbial growth. In the same experiments two processes can be identified by their sulfate oxygen isotope values, one of which predomi-nates during lag phase growth. Despite the transience of the lag phase growth period we have detected these isotope signatures in the waters produced by pyrite oxidation in the Río Tinto system, southern Spain.

Lab oxidation of pyrite: We measured sulfur and oxygen isotope compositions of sulfate from pyrite oxidation, compared with those of pyrite and water, respectively. The samples used were those for which we had identified different chemical compositions of solutions during lag and exponential growth phase, the former characterized by having almost all iron present as Fe2+ [9]. Significant isotope fractionation occurs only in the lag phase of microbial growth where the predominant oxidation pathway is represented by FeS2 + 3.5O2 + H2O Fe2+ + 2SO4

2- + 2H+. Abiotic pyrite oxidation, catalyzed by ferric ion, FeS2 + 14Fe3+ + 8H2O 15Fe2+ + SO4

2- + 16H+, is the dominant path-way in the exponential growth phase and gives negli-gible sulfur and oxygen isotope fractionation while the microbes oxidize Fe2+to Fe3+. The sulfur isotope frac-tionation during the lag phase may result from dispro-portion of sulfoxyanion after dissolution of pyrite. 34S in sulfate is +4.3±0.6‰ relative to the pyrite. Oxygen isotope fractionation during lag phase growth is esti-mated as a maximum of approximately +13‰, 18O sulfate relative to water. Our simple mass balance cal-culations show that at least two mechanisms are oper-ating and contributing in different proportions during

the lag and exponential growth phases. The variations in previously published values are indeed most likely produced by differences in experimental conditions that could control the relative contributions of the two oxidation pathways. Thus, lag phase microbial oxida-tion of pyrite is characterized by presence of Fe2+ and relatively positive 18O values.

Río Tinto area field studies: Extensive analysis of chemical and isotopic compositions of waters of the Río Tinto basin has identified a multicomponent mix-ing system. Two main sources predominate. The first is typified by the headwaters at Peña del Hierro: a small volume of red, concentrated (Fe, 10-23 g/L), nearly fully oxidized (Fe2+ 3% of Fetotal), low pH (1.6-1.7) water. Iron speciation and microbial assays [10] imply pyrite oxidation by ferric iron with the re-leased Fe2+ being rapidly oxidized by L. ferriphilum and A. ferrooxidans. Our data show a fractionation of +4.0 ‰ in

18O-SO4 relative to water and suggest that water is the primary source of oxygen. The other main component is a green, lower pH (0.87 – 1.1), more concentrated (Fe, 8.1-46 g/L), reduced (Fe2+, 72-97 %) solution sampled at Zarandas Naya. 18O-SO4 is + 11.2-13.0 ‰, relative to the water and implies a major contribution from atmospheric oxygen, similar to that in lag phase growth. Since these solutions form Fe2+

sulfate evaporite minerals microbial oxidation biosig-natures may occur and be preserved.

Conclusions: Paradoxically, solutions like those from lag phase oxidation are produced persistently at Río Tinto. Their preservation as sulfate evaporites can offer an insight into past microbial processes.

References: [1] Squyres S.W. et al. (2004) Sci-ence, 306, 1709-1714. [2] Grotzinger J.P. et al. (2005) EPSL, 240, 11 –72. [3] Bibring J.-P. et al. (2006). Sci-ence, 312, 400-404. [4] Zolotov M. Y. and Shock E. L. (2005) Geophys. Res. Let., 32, L21203, 5pp. [5] Taylor B.E. et al. (1984) Geochim. Cosmochim. Acta, 48, 2669-2678. [6] Lloyd R.M. (1968) JGR, 73, 6099-6209. [7] Taylor B.E. et al. (1984) Nature, 308, 538-541. [8] Moses C.O. et al. (1987) Geochim. Cosmo-chim. Acta, 51, 1561-1571. [9] Yu J-Y et al. (2001) Chem. Geol., 175, 307-317. [10] Gonzalez-Toril E. et al. (2003) Appl. Env. Microbiol., 69, 4853-486.


SULFATE STABILITY UNDER SIMULATED MARTIAN CONDITIONS. M. Craig, E. A. Cloutis, Depart-ment of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9 ([email protected], [email protected]).

Introduction: Spectral properties of a number of

sulfate samples, 450 to 2500 nanometers, have been investigated under simulated Mars surface conditions of atmospheric pressure and composition, ultraviolet light regime and limited temperature regulation in the Planetary Spectrometer Facility at the University of Winnipeg.

Experimental Procedure: Reflectance spectra of the <45 µm samples were acquired with an ASD Field-Spec Pro HR from 450-2500 nm with between 2 and 7 nm spectral resolution via bifurcated fibre optic probe i=0º, e=0º relative to halon. Two thousand spectra were averaged to increase signal-to-noise ratio. Re-flectance spectra from 2-4.3 µm were measured with a Designs and Prototypes Model 102F FTIR spectrome-ter with i=35°, e=0° and 6 wavenumber resolution, relative to brushed gold. One hundred spectra were averaged to reduce signal-to-noise ratio. Reference spectra were measured in air, without the sapphire window of the environment chamber, then with win-dow prior to and immediately following pump down to 5 torr CO2 (0.2 inHg, 6.7 Mb). Spectra were collected approximately every two days thereafter as well as be-fore and after each change in experimental conditions. Standard procedure has been a run of 10 days at 5 torr, 10 days at 5 torr plus irradiation by ultraviolet light (1 day = 1 decade on Mars) and 10 days at lower pres-sure, 2e-2 to 8e-3 torr CO2; excepting samples from the first run which spent 14, 9 and 24 days at equivalent conditions, respectively. The samples were kept be-tween 12º and 26ºC throughout.

Results: Presented in figure 1 are the reflectance spectra of four samples (normalized to 1 at 1.25 µm), from top to bottom: gypsum (run 1), hexahydrite 1 (run 1), hexahydrite 2 (run 3) and kieserite (run 2). Not shown are corresponding spectra from 2-4.3 µm and spectra from samples that evidenced little or no changes: jarosite (run 1), anhydrite, alunite, szomol-nokite, fibroferrite, paracoquimbite, copiapite and rhomboclase (run 2) and gypsum (run 3). What dif-fered between runs other than overall duration was vacuum level of the lower pressure portion. Ultimate vacuum achieved for runs 1 thru 3 was 8e-3, 1e-2 and 2e-2 torr, respectively.

Discussion: The results of exposure to current Martian surface conditions have been vastly different on the series of sulfates studied. The H2O bearing members have experienced the most spectral changes due to dehydration with both decreases in hydration

feature band depth, and subtle shifting to lower wave-lengths of some band centers. The OH and H2O/OH free samples evidenced no changes with exposure to 5 torr and 5 torr with UV. Dehydration did not occur in any samples until the pressure was lowered below 5 torr and preceded very rapidly thereafter if a particular sample’s vacuum threshold was crossed. This effect is most evident in the two identical gypsum samples. The sample from the first run dehydrated very rapidly at 8e-3 torr but did not dehydrate at all at 2e-2 torr.

Conclusions: This study raises several questions, some of which we cannot yet answer. Exposure to 5 torr of such short duration has no discernable effect on the sulfates studied thus far; as such, does exposure to lower pressures approximate a vastly longer time span at 5 torr? Additionally, what are the effects of the di-urnal/seasonal temperature swings on Mars?

Figure 1: From top to bottom: gypsum, hexahy-drite 1, hexahydrite 2 and kieserite. Black, first spec-tra acquired in air with window, red, last spectra ac-quired with window at 8e-3, 8e-3, 2e-2 and 1e-2 respec-tively. Only first and last spectra shown for clarity.


MIXING AND RE-SOLUTION PROCESSES AFFECTING EVAPORITE MINERAL DISTRIBUTIONS ON EARTH AND MARS. J. K. Crowley1, J. S. Kargel2, G. M. Marion3, S. J. Hook4, N. T. Bridges4, A. J. Brown5 and C. R. de Souza Filho6 1 U. S. Geological Survey, MS 954, Reston, VA 20192, [email protected] 2 University of Arizona, Tucson, AZ, [email protected] 3 Desert Research Institute, NV, [email protected] 4 Jet Propulsion Laboratory, CA, [email protected], [email protected] 5 Ames Research Center, CA, [email protected] 6 U. of Campinas, S.P., Brasil, [email protected]

Introduction: Near-surface groundwaters that

freeze or evaporate produce saline mineral assem-blages that are generally related to the initial dissolved solute compositions [1]. Such assemblages formed by the fractional crystallization of evaporating brines are composed mainly of phases that represent major chemical divides, and these assemblages can be readily predicted by chemical modeling [2], [3]. Here we highlight several additional processes that can mark-edly increase evaporite assemblage complexity on Earth and likely also on Mars. Temporal oscillations in these processes can produce evaporite laminations and beds.

Dilute Inflow Additions to Brine: During the course of groundwater evolution certain solutes are typically depleted. A classic terrestrial example is potassium, which is removed from groundwaters by clay mineral adsorption. Even major solutes such as calcium may be depleted via the action of chemical divides. However, playa-margin springs and ephemeral streams provide inflow sources of dilute, unevolved waters that may discharge directly into more concen-trated brines. A similar source function may be served on Mars by permafrost melting during warm climatic shifts or by impact heating or hydrothermal activity. These sources “short-circuit” the normal course of brine evolution and produce mineral assemblages con-taining “unexpected” solute components.

Volcanic Exhalative and Hydrothermal Addi-tions to Brine: In terrestrial playa settings, and hypo-thetically also on Mars, some springs have water sources and solute compositions that are very different from typical basinal groundwaters. For example, spring waters enriched in borate produce distinctive evaporite mineral assemblages and at the same time signal the existence of deeper circulating, perhaps hydrothermal, water sources.

Zone Refining: Another way that unusual brine compositions are produced is by passage of concen-trated brines through thick sequences of evaporitic materials; already saturated major mineral species re-main stable, but minor and trace species are progres-sively leached and fractionated into the brine until they too, saturate. Salts enriched in K, Rb, Sr, Br, I, B, and other elements can be produced this way. On Mars, where rainfall washing and re-solution of precipitated

salts has been minimal or absent through much of geo-logic time, zone refining in subsurface saline ground-water/evaporite systems or in surficial duricrusts may have produced long-lasting deposits of exotic salt compositions.

Re-cycling of Evaporite Crusts: Partial re-solution of evaporite crusts-- a process that includes zone refining but includes other processes, too-- also can lead to increased mineral diversity. For example, Mg is present in many terrestrial salt crusts as highly soluble chloride phases that are easily leached and redistributed. However, in sulfate-rich brines, perhaps akin to those on Mars, Mg is more resistant under some circumstances. On Mars, we expect that incon-gruent dissolution-- peritectic melting of hydrates with partial dehydration of residual salts-- is apt to be even more important than on Earth, because the higher hy-dration states are expected to be more common. In fact, crustal re-cycling outcomes are complexly de-pendent on parent brine compositions.

Redox and pH Cycling: Special types of geo-chemical divides are represented by the buffering of pH and redox state by major mineral or dissolved spe-cies. When acid/base or reductant/oxidant titration occurs, buffers eventually can be overwhelmed and brine equilibria can suddenly shift, additional species can be solubilized or precipitated out of solution, and mineral stability completely altered. This type of be-havior can occur in response to oscillations in brine sources and brine mixing, episodes of igneous rock emplacement in the catchment basin, volcanic exhala-tive activity, erosional exhumation and weathering of different rock types, or shifts in atmospheric composi-tion.

Terrestrial acid evaporite mineral deposits are one of several Mars-analog environments being studied by the authors in the field and through chemical model-ing.

References: [1] Eugster H. P. and Hardie L. A. (1980) in Lakes:

Chem. Geol. Phys., Springer-Verlag, N. Y., 237-293. [2] Tosca N. J. and McLennan S. M. (2006) Earth Plan. Sci. Let., 241, 21-31. [3] Marion, G.M., et al. (2003) Geochem. Cosmochim. Acta, 67, 4251-4266.


Sulfate Brine Stability Under a Simulated Martian Atmosphere J Denson1, V. Chevrier1, D.W.G. Sears1, 1W.M. Keck Laboratory for Space Simulations, Arkansas Center for Space and Planetary Sciences, 202 Old Museum Building, University of Arkansas, Fayetteville, AR 72701, USA <[email protected], [email protected], [email protected]>.

Introduction: Liquid water is thought to be

unstable on the surface of Mars. However given that the surface conditions are close to the triple point of water under the appropriate conditions, liquid water could form and remain at least metastable for brief periods of time [1]. Various observations of recently formed gullies support this hypothesis [2].

The predictions of the Ingersoll [3] equation agree with previous experimental studies addressing the evaporation rates of pure water [4] as well as NaCl and CaCl2-bearing brines [5]:

31

2612.0

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡ Δ

Δ=νρρ

ηρg

DE atm

where E is the evaporation rate in mm/h, Δη is the concentration difference at the surface of the sample and at distance, ρatm is the atmospheric density, D is the diffusion coefficient for water in CO2, g is acceleration due to gravity, and ν is the kinematic viscosity of CO2.

Previous studies have shown that brines could stabilize liquid water on Mars by lowering the eutectic point of the solutions [6], as well as their evaporation rate [5]. Recently obtained visible-near infared spectral data has added additional support suggesting the presence of sulfates on Martian surface [7]. The specific goal of this series of experiments is to investigate the stability of MgSO4 brines under simulated Martian conditions. In the case of sulfate brines ions are more highly charged than for NaCl solutions [5] therefore ionic interactions will be stronger, which should influence the activity of water. Evaporative experiments were performed under silmulated Martian conditions; 5-7 mbar, pure CO2 atmosphere and 0°C.

Conclusions: Numerous experiments were conducted to investigate the stability of MgSO4 brines of varying concentrations under simulated Martian conditions. Crystallization was observed at high brine concentrations leading to a dramatic effect on the stability of water under these conditions. Therefore, in addition to the chemical effect of highly concentrated brines, the crystallization of salts strongly sztabilizes the brine. The hydration state of these crystals is currently being investigated utilizing X-Ray diffraction. This study provides initial evidence that

sulfate minerals could conceivably serve as a reservoir of surface and subsurface water on the Mars.

References: [1] Richardson M. I. and Mischna M. A. (2005) J. Geophys. Res., 110, doi.10.1029/2004 JE002367. [2] Heldmann J. L. et al. (2005) J. Geophys. Res., 110, doi.10.1029/2004JE002261. [3] Ingersoll A. P. (1970) Science, 168, 972-973. [4] Sears D. W. G. and Chittenden J. D. (2005) Geophys. Res. Lett., 32, doi.10.1029/2005GL024154. [5] Sears D. W. G. and Moore S. R. (2005) Geophys. Res. Lett., 32, doi.10.1029/2005GL023443. [6] Brass G.W. (1980) Icarus, 42, 20-28. [7] Gendrin A. et al. (2005) Science, 307, 1587-1591.

0.88

0.90

0.92

0.94

0.96

0.98

1.00

0 20 40 60 80 100 120

Time (mn)

Rel

ativ

e m

ass

data

Ingersoll pure water

MS7

MS12

Figure 1. 20 wt% brine solution and fit with the predicted Ingersol derived rate for the evaporation of MgSO4.7H2O (MS7) and MgSO4.12H2O (MS12),

0.95

0.96

0.97

0.98

0.99

1.00

0 20 40 60 80 100 120

Time (mn)

Rel

ativ

e m

ass

data

Ingersoll pure water

Series1

Linear (Series1)

Figure 2. 20 wt% brine solution corresponding with the Ingersol equation initially, before diverging with a dramatically decreased rate of evaporation. Crystallization of the sulfates was observed in the sample.


MÖSSBAUER SPECTROSCOPY OF SYNTHETIC ALUNITE GROUP MINERALS. M.D. Dyar1, L. Po-dratz2, E.C. Sklute1, C. Rusu1, Y. Rothstein1, N. Tosca3, J.L. Bishop4, Lane, M.D.5. 1Dept. of Astronomy, Mount Holyoke College, South Hadley, MA, 01075; [email protected]. 2Dept. of Geosciences, Stony Brook Univ., Stony Brook, NY. 3Dept. of Geological Sciences, Univ. of Idaho, Moscow, ID. 4SETI Institute/NASA-Ames Re-search Center, Mountain View, CA. 5Planetary Science Institute, Tucson, AZ.

Introduction: The alunite mineral group includes

(among others) six common rock-forming minerals: alunite KAl3(SO4)2(OH)6 natroalunite NaAl3(SO4)2(OH)6 schlossmacherite (H3O,Ca)Al3[(SO4,AsO4)2(OH)6 jarosite KFe3+

3(SO4)2(OH)6 natrojarosite NaFe3+

3(SO4)2(OH)6 hydronium jarosite H3OFe3+

3(SO4)2(OH)6 Solid solutions among these six minerals represent possible combinations of the cations Al and Fe3+ in the 6-coordinated site of the structure, and K, Na, and H3O+ (hydronium) in the 9-coordinated site. The goal of this project is to determine the crystallographic and spectroscopic characteristics of these different miner-als as a function of composition – in the hope that compositions might be deduced on the basis of remote measurements. We are undertaking XRD, Mössbauer, visible-IR reflectance and mid-IR emittance measure-ments on synthetic compositions within the alunite group.

Samples: Our initial Mössbauer measurements [1] of jarosites focused on samples prepared by [2] and spanning the range from K-H3O+-rich jarosites. Addi-tional samples were synthesized at SUNY and were obtained from the laboratory of A. Navrotsky at UC Davis (from [3] and others). More than 60 different compositeons have been synthesized to date and many more are planned (Fig. 1).

Results: Mössbauer spectra of synthetic samples in some cases show the presence of multiple doublets (quadrupole splitting distributions) representing multi-ple nearest and next-nearest neighbor environments surrounding the octahedral Fe3+ cations. They have parameters of IS (isomer shift) = 0.37-0.39 mm/s in all cases, but two groups of QS (quadrupole splitting) from 1.13-1.30 mm/s and 0.37-0.97 mm/s.

Trends between Mössbauer parameters and compo-sition are most evident with regard to QS. In jarosite-alunite and natrojarosite-natroalunite solid solutions, low Fe (0.5 pfu) favors high QS (1.30 mm/s), while high Fe (3 pfu) gives rise to QS =1.15 mm/s. In the jarosite to hydronium jarosite series, QS increases from 1.08 to 1.28 mm/s as K increases from 0.47 to 0.86 pfu. However, these trends reflect variations in only two of the five possible compositional variables for this mineral group. Combinations of all five vari-ables (Al, Fe3+, K, Na, and H3O+) do not yet show con-

sistent trends with Mössbauer parameters. Work is ongoing to refine these results and compare them with other types of spectroscopic measurements.

Fig. 1. Ternary diagram of the K-Na-H3O+ system pro-jected from the jarosite (Fe3+) to the alunite (Al3+) compo-sition space. Brophy samples [2] are shown as red cir-cles, UCD samples as triangles [see text], and SUNY sam-ples [this study] as squares.

Implications for Mars: The Mars Exploration Rover (MER) Mössbauer spectroscopy team identified jarosite in spectra of a layered outcrop in Meridiani Planum [4] based on a doublet with quadrupole split-ting of ~1.22 mm/s (or ~1.20 mm/s at 293K) that was assigned to either K- or Na-jarosite with Al possibly substituting for Fe in octahedral sites. The best matches of these parameters to samples in our current data set include three very different compositions:

~Na1Fe0.76Al2.24(SO4)2(OH)6, ~Na0.72-0.78H3O+

0.27-0.19Fe3+3(SO4)2(OH)6, and

~K0.67-0.70H3O+0.29Fe3+

3(SO4)2(OH)6. Fe3+ in other sulfates such as botryogen, rosenite, sideronatrite, and ferricopiapite may also have these same parameters. We hope that further study of our new large jarosite-alunite collection will enable us to better constrain the composition of the MER results.

References: [1] Rothstein Y. et al. (20060 LPSC XXXVII, Abstract #1727. [2] Brophy, G.P. & Sheridan, M.F. (1965) Amer. Mineral., 50, 1595-1607. [3] Drouet C. et al. (2004) GCA 68(10), 2197-2205. [4] Klingelhöfer G. et al. (2004) Science 306, 1740-1745.


Lifetime of jarosite on Mars: preliminary estimates. M.E. Elwood Madden1 and J. D. Rimstidt2, 1 Oak Ridge National Laboratory, Oak Ridge, TN 37830, [email protected]; 2Dept. of Geosciences, Virginia Tech, Blacksburg, VA 24061, [email protected].

Introduction: Observations of alteration assem-

blages containing sulfate minerals (including jarosite- the focus of this study), iron (hydr)oxides and perhaps halides by the Mars Exploration Rovers (MER) within sedimentary rocks at Meridiani Planum and the Co-lumbia Hills provide direct evidence that Mars surface rocks have been chemically weathered by liquid water at some point in their history [1-3]. However, the pres-ence of jarosite, a metastable phase [4], suggests that liquid water was removed from the system before the alteration fluid equilibrated with mafic surface materi-als and reached neutral or alkaline pH [1], [5], [6]. Jarosite will begin to convert to goethite or hematite (both of which are thermodynamically stable phases relative to jarosite) upon formation, and will continue to convert to form an iron (hydr)oxide as long as liquid water is present [4]. The presence of jarosite in altera-tion assemblages at Meridiani Planum and possibly Gusev Crater indicates that water was removed from these systems before jarosite could fully convert to hematite [1]. Using jarosite dissolution rate data avail-able in the literature we have calculated estimated jarosite lifetimes for a range of initial particle sizes.

Jarosite dissolution rates: Analysis of dissolution rates available in the literature and explicit rate studies result in a range of dissolution rates differing by nearly three orders of magnitude. Gasharova et al. [7] di-rectly measured the dissolution rate of jarosite, yield-ing a rate of 1.45x10-7 mol m-2 s-1 at pH=5.5. They also reexamined dissolution data collected by Baron and Palmer [8] at pH = 2 and calculated a dissolution rate of 3x10-9 mol m-2 s-1. Based on their measurements and the recalculated rates from Baron and Palmer, Gasharova et al. suggest that the dissolution rate is pH dependent. However, dissolution data presented by Smith et al. [9] suggests that the rate of jarosite disso-lution is relatively independent of pH (~ 4x10-10 mol m-2 s-1 at pH = 2; ~ 2x10-10 mol m-2 s-1 at pH = 8).

Estimating particle lifetimes: Assuming that each particle is a simple sphere, the lifetime of an indi-vidual jarosite particle was calculated using the equa-

tion: rV

dtm2

=

where t is the lifetime of the particle (sec), d is the di-ameter of the particle (m), Vm is the molar volume of the mineral (m3mol-1), and r is the rate of dissolution (mol m-2 sec-1). The resulting particle lifetimes using the full range of laboratory dissolution rates found in

the literature vary from 1-500 years for a 1mm diame-ter particle (Figure 1). However, dissolution rates in the field are often observed to be 2-3 orders of magni-tude slower than those observed in laboratory experi-ments [10], suggesting that lifetimes for 1mm particles in the field could reach 0.5 million years. In addition, lower temperatures and differing jarosite composi-tions, as well as variations in the pH, ionic strength, and hydrodynamics of the aqueous solution may result in significant changes in dissolution rates and pre-dicted lifetimes. The dissolution data available in the literature cover a narrow range of temperatures, pH, ionic strengths, and compositions. Additional studies to determine the dissolution rate of jarosite under Mars-relevant conditions are needed to further con-strain jarosite lifetimes and hence the duration of liq-uid water in jarosite-bearing sediments. References: [1] Elwood Madden et al. (2004) Nature, 431, 821-823 [2] Squyers et al. (2004) Science, 306, 1709-1714. [3] Haskin et al. (2005) Nature, 436, 66-69. [4] Langmuir (1997) Aqueous Environmental Geochemistry [5] Tosca et al. (2005) EPSL, 240, 122 148, [6] Fernandez-Remolar et al. (2005), EPSL, 240, 149-167 [7] Gasharova et al. (2005) Chem.Geol, 215, 499-516, [8] Baron and Palmer (1996) Geochim. Cosmochim. Acta, 60, 185-195, [9] Smith et al. (2006) Geochim. Cosmochim. Acta, 70, 608-621. [10] White and Brantley (1995) Rev. Mineral., 31, 1-21.

Figure 1. Preliminary estimates of jarosite particle life-times on Mars based on laboratory dissolution rates from [7-9]. Geochemical reaction rates are often observed to be 2-3 orders of magnitude slower in the field, resulting in a similar increase in particle lifetimes [10].


SULFATE FORMATION AND ITS RELEVENCE TO ENVIRONMENTAL CONDITIONS ON EARLY MARS C. Fan1, D. Schulze-Makuch1 and H. Xie2, 1Dept. of Geology, Washington State University ([email protected]), 2Dept. of Earth and Environmental Sciences, University of Texas at San Antonio.

Introduction: A variety of sulfates, hydrated

phyllosilicates, and iron oxides were detected by OMEGA/MEX, TES/MGS and the Mars Rovers Opportunity and Spirit. These observations provide fresh insights into Martian surface processes at a specific time of Martian geological history. We suggest a mechanism of formation of sulfates and associated minerals based on the occurrence of sulfates on Mars, the conservation of mass, and the solubility of sulfates. We draw conclusions about the role of water in regard to Martian surface process and its implication for Martian life.

Background and Discussion: Kieserite (MgSO4·H2O) and epsomite (MgSO4 ·7H2O), gypsum (CaSO4.2H2O) or bassanite (2CaSO4 ·H2O), and copiapite [Fe2+Fe4

3+ (SO4)6(OH)2 ·20H2O] or halotrichite [Fe2+Al2(SO4)4·22H2O], and likely halite (NaCl) have been detected through hyperspectral images in numerous areas of Mars by the ESA OMEGA team [1] [2] [3]. Jarosite [KFe3 (SO4)2(OH)6] and the iron oxide hematite (Fe2O3) were identified through TES/MGS and the Opportunity rover [4]. The layered sulfate deposits on Mars as revealed from MOC images and the HRSC/MEX camera [1] [2] indicate that they were formed by precipitation in acidic brine as evaporites. The mechanism is consistent with the formation of sulfates essentially occurring on Earth, and is difficult to be interpreted otherwise.

Precipitation of sulfates from brine is controlled by the contents of cation and anion solutes, the solubility of their aqueous complexes, and temperature, pressure and pH value. Sulfates deposits accumulate when sulfates are oversaturated and the solution condenses due to evaporation of water or the influx of solutes. Solubility of sulfates is the main factor determining the sequence of different sulfate deposits given relatively constant thermodynamic conditions. Different sulfates have different solubility, which increases from magnesium-, calcium-, iron- to aluminum sulfates; the main sulfates detected on Mars until now. Metal cations are likely derived from a thick mantle of phyllosilicate deposits of weathered basaltic crust. Abundant deposits of phyllosilicates and other hydrated minerals were detected on Mars, and are overlain by volcanic lava flows [5] [6]. The dominant sulfates detected are consistent with the major components of altered mafic igneous rocks, which are Mg, Fe Ca, Al and Na [7]. Anions are presumed to be brought up by fluids associated with volcanic activities

such as near Tharsis Montes, and are thought to be dominated by SO4

2-, but Cl- and others anions can not be ruled out. A very thin CO2-dominated atmosphere may have contributed some CO2 to the initial solution, but HCO3

- and CO32-are likely negligible.

Several lines of evidence indicate that the fluid brought up by the volcanic activity between the “phyllosian” and “theiikian” era made some relatively isolated water bodies very hot and acidic dissolving weathered and unweathered basaltic crust. As water evaporated into space and temperatures decreased, major metal ions and sulfates became more and more enriched and finally became oversaturated. Magnesium sulfates such as kieserite and epsomite started to precipitate first due to their lower solubility in respect to other sulfates. Calcium sulfates such as gypsum precipitated following kieserite and overlying it, which is indicated by sulfate-rich layered deposit at Juventae Chasma, Valles Marineris [1]. Iron sulfates and aluminum sulfates precipitated when magnesium and calcium were almost fully consumed in the brine. Finally, a majority of sulfate ions had likely been consumed at this time, thus any remaining iron was deposited in form of oxides (the so-called “blueberries” detected in Meridiani Planum). Halite likely precipitated at this time when chlorine was relatively concentrated in solution due to the depletion of sulfate ions. The precipitation of sulfates overlapped with transient boundaries.

Conclusion: The sequence of sulfate formation suggests that the Martian surface was warm and spotted with standing bodies of liquid water during a span of time in Martian early history. Acidic hot water bodies may be associated with the origin and persistence of life on Earth. If so, the sites on Mars with confirmed sulfate deposits are promising targets for the exploration of Martian life.

References: [1] Bibring J.P. et al. (2005) Science, 307, 1576–1581. [2] Gendrin A. et al. (2005) Science, 307, 1587–1591. [3] Langevin Y. et al. (2005) Science, 307, 1584–1586. [4] Klingelhofer G. et al. (2004) Science, 306 1740-1745. [5] Poulet F. et al. (2005) Nature, 438, 623–627. [6] Bibring J.P. et al. (2005) Science, 312, 400–404. [7] Mustard J.F. et al. (2005) Science, 307, 1594-1597.


RAMAN IMAGING ANALYSIS OF JAROSITE IN MIL 03346. M. Fries1, D. Rost2, E. Vicenzi2 and A.Steele2, 1Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington,DC, 20015 [email protected], 2National Museum of Natural History, Smithsonian Institution, Washington, D.C.20013

Introduction: The nahklite MIL 03346 is an or-thopyroxene cumulate noted for bearing evidence offaster cooling than other known nahklites, possiblyindicative of relatively shallow placement in Mars’crust. The mesostasis includes hematite, cristobaliteand skeletal olivine-composition silicates within afeldspathic glass mesostasis. Recent imaging Ramananalysis has identified jarosite veins crosscutting andmantling both skeletal and euhedral olivine grains.

Introduction: Raman spectroscopic imaging wasperformed at the Geophysical Laboratory using aWITec α-SNOM customized to include Raman imag-ing. Excitation was via a 532-nm wavelength laserwith a pixel size of 360nm2 and spectral resolution ofaround 4 cm-1. Images were collected of mesostasisassemblages in two MIL 03346 thin sections withcomparable findings.

Results: Raman imaging identifies silica blebsnoted elsewhere [1] as cristobalite and an unknownolivine-composition phase intergrown with fayalite [2].Jarosite is found predominantly in association witholivine assemblages as both transgranular and mantlingveins. This mineral was discovered independentlyusing EMP X-ray mapping, and co-located EMP andRaman analyses show agreement in phase identifica-tion and spatial distribution [3].

Discussion: The origin of jarosite in MIL 03346cannot be definitively determined from current data,although Herd’s [3] observation that jarosite veinscrosscut iddingsite alteration products may imply aMartian origin. Additionally, Raman imaging meas-urements seem to show that jarosite resides only withinMIL 03346 mesostasis, arguing for formation by smallscale alteration of mineralogy rather than by jarositeaqueous transport. It should be noted that this obser-vation does not preclude jarosite deposition throughterrestrial aqueous alteration, and jarosite has beennoted in Antarctic micrometeorites [4]. This indicatesthat a mechanism exists for jarosite formation via Ant-arctic melt water infiltration. Further work, perhaps byisotopic analysis methods, will be necessary to estab-lish the origin of this mineral.

References: [1] Anand M et al (2005) LPSCXXXVI Abstract 1639, [2] Rost D., Vicenzi E., FriesM. and Steele A., (2006) LPSC XXXVII Abstract2362. [3] Herd C., This volume. [4] Osawa et al (2003)MAPS 38, pp. 1627-1640.

Figure 1. Upper figure: Reflected light microscopyimage of MIL 03346 skeletal olivine assemblage withRaman image overlay. The red/yellow image is ajarosite 1010 cm-1 peak intensity map showing phasedistribution. Note the presence of jarosite as a crack-filling material. Center figure: Variation of Raman O-H stretch mode for the same image, indicating minorvariation of (OH-) concentration. Lower figure: An-notated Raman spectrum of jarosite from MIL 03346.


MARTIAN AND ST. LUCIAN JAROSITE: WHAT WE CAN LEARN ABOUT MERIDIANI FROM AN

EARTH ANALOGUE. J. P. Greenwood1, M. S. Gilmore

1, A. M. Martini

2, R. E. Blake

3, M. D. Dyar

4, J. A. Gil-

more5, and J. Varekamp

1,

1Dept. of Earth & Environmental Sciences, Wesleyan University, Middletown, CT 06459

([email protected]), 2Dept. of Geology, Amherst College,

3Dept. of Geology & Geophysics, Kline Geol-

ogy Laboratory, Yale University, New Haven, CT, 4Dept. of Astronomy, Mount Holyoke College, Holyoke, MA,

5Brooklyn, NY.

Our group has been studying the fumarolic envi-

ronment of the Sulphur Springs, St. Lucia, W.I., since

2000 [2,3,4]. In 2004, we discovered jarosite at sev-

eral locations within the caldera and have been con-

ducting a detailed survey of its occurrences and ab-

sence throughout the bubbling mudpots and boiling

pools of the site. Jarosite is currently forming at sev-

eral locations, affording us the opportunity to not only

collect jarosite in its geological and microbiological

context, but the waters from which it forms. We have

been able to apply a dizzying array of techniques to

study jarosite, both in the field and in the laboratory

(e.g. SEM/EDS, EPMA, vis/NIR, XRD, Mössbauer,

SIRMS, IC, ICP-AES, ICP-MS). This has given us

greater appreciation for the difficulty of extracting use-

ful information regarding jarosite and past fluid activ-

ity on Mars from limited remote spacecraft observa-

tions.

Jarosite on Mars vs. St. Lucia: To form jarosite

in any environment, several basic ingredients are nec-

essary. Low pH, high fO2, Fe3+

and SO4 in solution are

all needed. What also seems necessary is a lack of

buffering capacity of the existing strata. In St. Lucia, a

highly silicized andesitic to dacitic tuff is the dominant

rock type that jarosite forms veins in, away from the

main fumarolic area. In the main fumarolic area,

jarosite exists as encrustations on the top surfaces of

exposed rocks and cobbles. One location, dubbed Iron

Mountain Terraces (IMT), is especially illuminating as

goethite forms on jarosite-rich rocks. In this sample,

jarosite does not appear to be breaking down to form

goethite, but goethite appears to be precipitated as lay-

ers on the existing jarosite-bearing strata. This calls

into question wheter a genetic relationship between

jarosite and iron oxide (hematite) exists at Meridiani,

or as is the case in St. Lucia, changing fluid conditions

lead to a change in how iron precipitated from solution

(at St. Lucia, rainfall events lead to higher pH fluids,

which precipitate goethite vs. jarosite during wetter

times).

Determining the composition and water content of

jarosite in St. Lucia has been challenging. For exam-

ple, Mössbauer parameters on newly formed jarosite

(<1 year) closely resemble those of a synthetic jarosite

w i t h a c o m p o s i t i o n o f

K0.70Na0.01(H3O+)0.29Fe3(SO4)2(OH)6 [5]. Rietveld re-

finement to determine unit cell parameters are in broad

agreement with Mössbauer of this sample, but quanti-

tative electron microprobe results were not possible

due to the fine-grained and hydrous nature of the the

jarosite. EPMA has been very difficult on all samples

of jarosite at St. Lucia due to the hydrous and fine-

grained character of this mineral.

Stable isotope studies of jarosite were found to be

necessary to elucidate the conditions of jarosite forma-

tion at St. Lucia [3]. On Mars, this will likely neces-

sitate sample return, and will be a difficult geochemi-

cal problem due to mass-independent sulfur and oxy-

gen isotope systematics. An advantage of studying

jarosite from St. Lucia is that we can undertake studies

of the fluids from which jarosite likely precipitates.

Fluid geochemical analyses and modeling combined

with stable isotope studies of these fluids (!18

O and !D

of water; !34

S and !18

O of dissolved SO4 and !34

S of

dissolved H2S) allow us a window into jarosite forma-

tion that will likely never be possible at Mars. Yet, we

still have difficulties understanding many aspects of

jarosite formation in St. Lucia. Current work is now

focused on understanding the stable isotopes of water

in various sites within the jarosite structure in hope of

using the oxygen in sulfate and OH geothermometer

[6].

Summary: Jarosite forms in a number of different

settings at St. Lucia. Evaporation of acidic fluids is

one mode of current jarosite formation. Jarosite for-

mation in veins in porous rock is another mode. We

see no evidence of jarosite being hydrolyzed to iron

oxides at this site. Iron oxide minerals instead precipi-

tate from solutions that have been diluted by recent

rain. At Meridiani, jarosite formation is likely AFTER

hematite concretions due to the instability of jarosite in

putative Martian brines [7]. Jarosite mineralization

after hematite concretion is in keeping with the time-

line of Bibring et al. (2005) [8], which calls for a

planet-wide acid-sulfate event after a more circum-

neutral to basic hydrosphere.

References: [1] Klingelhöfer G. et al. (2004) Science,

306, 1740-1745. [2] Greenwood J. P. et al. (2002) LPSC

XXXIII, Abstract# 2037. [3] Greenwood J. P. et al. (2005)

LPS XXXVI, Abstract# 2348. [4] Greenwood J. P. et al.

(2006) LPS XXXVII Abstract# 2230 [5] Rothstein Y. et al.

(2006) LPS XXXVII Abstract# 2216. [6] Rye R. O. (2005)

Chem. Geol. 215, 5-36. [7] Barrón et al. (2006), this meeting.

[8] Bibring P. et al., (2005) Science, 307, 1576-1581.


CATHODOLUMINESCENCE STUDY OF PHOSPHATES IN THE Y000593 NAKHLITE. A. Gucsik1, H. Nishido2, K. Ninagawa3, T. Okumura2, N. Matsuda2, M. Kayama2, J. Götze4, J. Z. Wilcox5, Sz. Bérczi5, Á. Keresz-turi5 and H. Hargitai5 1University of West Hungary ([email protected]), Bajcsy-Zs. u. 4., Sopron, H-9400, Hungary; 2Okayama University of Science, Research Institute of the Natural Sciences, 1-1 Ridai-cho, Oka-yama, 700-0005, Japan; 3Okayama University of Science, Department of Applied Physics, 1-1 Ridai-cho, Okayama, 700-0005, Japan; 4TU Bergakademie Freiberg, Brennhausgasse 14, D-09596 Freiberg, Germany; 5Jet Propulsion Laboratory (JPL)-Caltech, 4800 Oak Grove Drive, Pasadena, CA 91109, U.S.A; 6Eötvös Lorand University of Bu-dapest, H-1117 Budapest, Pázmány Péter sétány 1/c., Hungary

Introduction: Cathodoluminescence (CL) is an emis-sion of the visible light stimulated by high energetic electrons. In the previous studies of CL properties of the Martian meteorites, it was demonstrated that its detection system provides a more complete investiga-tion of specific minerals [1,2]. The main purpose of this study is to provide detailed mineralogical informa-tion on the phosphates in Martian meteorites, espe-cially in nakhlites..

Samples and Experimental Procedure: We stud-ied a polished thin sections of the Y000593 nakhlite Martian meteorite supplied from the National Institute of Polar Research (NIPR, Tokyo, Japan). SEM-CL imaging and CL spectral analyses were performed on the selected thin sections coated with a 20-nm thin film of carbon in order to avoid charge build-up. SEM-CL images were collected using a scanning electron mi-croscope (SEM), JEOL 5410LV, equipped with a CL detector, Oxford Mono CL2, which comprises an inte-gral 1200 grooves/mm grating monochromator at-tached to reflecting light guide with a retractable paraboloidal mirror. The operating conditions for all SEM-CL investigation as well as SEM and backscat-tered electron (BSE) microscopy were 15 kV acceler-ating voltage, and 3.0-5.0 nA beam current at room temperature. CL spectra were recorded in the wave-length range of 300-800 nm, with 1 nm resolution by the photon counting method using a photomultiplier detector, Hamamatsu Photonics R2228.

Results and Discussion: Apatite (Ap) was found as a mesostasis mineral in the nakhlite meteorite, which occurs in veins between mostly clinopyroxene (Cpx) and plagioclase (Pl). Detailed mineralogical description of the Y-000593 nakhlite can be found in Imae et al [3]. This mineral appears in the nakhlite as yellow CL color in the Luminoscope images and CL-bright areas in the SEM-CL images. The CL spectral results are preliminary and the peaks have been identi-fied as indicated by the previous CL spectral analysis of apatite [4-7]. These results indicate that apatite is chloroapatite, which is an anhydrous phosphatecon-taining unfamiliar anions F, Cl, O, OH, cations of me-dium and large size: Mg, Cu, Zn, and Ca, Na, K, Ba, Pb.

Conclusion: Consequently, the more aspect is that CL spectroscopy combined with SEM-CL imaging is a potentially powerful technique in the study of phospa-hets. We would also like to demonstrate that CL tech-nique can play a key role in the in-situ investigations of records of the atmospheric-fluid-rock interactions such as formation of sulphates, carbonates, and phos-phates. In our study of cathodoluminescence properties of the apatite of the nakhlite sample, we did not observe any new phases of this mineral occurred at high tempera-ture.

Acknowledgement This work partly supported by

the Hungarian Space Organization (TP-293) and the Working Group of the Space and Planetaty Sciences at the Hungarian Academy of Sciences. We are also thankful for Prof. Kojima at NIPR (Tokyo, Japan) of-fering a set of the Martian meteorite samples.

References: [1] Protheroe W. J., Jr. and Stirling J.

A. R. (2000) LPS XXXI, Abstract #1980. [2] Protheroe W. J., Jr. and Stirling J. A. R. (2000) LPS XXXI, Ab-stract #2021. [3] Imae N. et al. (2005) Meteoritics & Planet. Sci., 40, 1581-1598. [4] Barbarand J. and Pagel M. (2001) Amer. Min. 86, 473-484. [5] Hayward C.L. (1998) Cathodoluminescence of ore and gangue min-erals and its application in the minerals industry, In: Cabri L.J., and Vaughan D.J. (Eds.) Modern Ap-proaches to Ore and Environmental Mineralogy, Min-eralogical Association of Canada Short Course Series, 27, 269-325. [6] Marshall D.J. (1988) Cathodolumi-nescence of geological materials. Unwin Hyman, Bos-ton, 146 pp. [7] Kempe U. and Götze J. (2002) Ca-thodoluminescence (CL) beheviour and crystal chem-istry of apatite from rare-earth deposits. Min. Mag.66. 151-172.


Trace elements in MIL 03346 jarosite: A record of martian surface processes? C.D.K. Herd, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada, [email protected].

Introduction: An occurrence of jarosite in the

Miller Range (MIL) 03346 nakhlite was suggested by electron microprobe (EMP) X-ray mapping [1], and has been confirmed by Raman spectroscopy [2]. This study involves a ToF-SIMS investigation of the distri-bution of a variety of trace elements among jarosite, iddingsite, and igneous phases.

Methods: Alteration products in MIL 03346 are typical of iddingsite in the nakhlites [3]; those associ-ated with skeletal, fayalitic (Fa88) mesostasis olivine in MIL 03346, 165 were examined in detail. The pres-ence of jarosite in this area was confirmed by Raman spectroscopy following the method of [2]. An ION-TOF IV (GmbH) Time-of-Flight Secondary Ion Mass Spectrometer (ToF-SIMS) was used to obtain positive and negative ion maps using a ~ 1 pA Ga primary beam. Integration times ranged from 20 to 60 minutes. Maps of a wide range of elemental and molecular ions were obtained with a resolution of < 1 µm.

Results: The distribution of jarosite from Raman mapping (according to [2]) agrees well with the distri-bution inferred from EMP X-ray mapping produced using image operations with the ImageJ software (K AND Fe AND S MINUS Si), as well as the distribution of K and SO4

2- ions from ToF-SIMS (Fig. 1). Jarosite occurs along fractures and grain boundaries, cross-cutting iddingsite alteration.

Is it martian? Jarosite has been reported as an al-teration product within Antarctic chondritic microme-teorites and the Yamato 793605 martian meteorite [4,5]; in both cases it is interpreted as the result of Ant-arctic aqueous alteration. Further studies are required to establish the origin of the MIL 03346 jarosite. Its presence implies oxidized and acidic conditions of aqueous alteration by S-rich brines [6]. Jarosite post-dates iddingsite formation, possibly reflecting evolu-tion of the hydrothermal system from neutral to acidic.

Implications for a record of surface processes on Mars: Regardless of its origin, the MIL 03346 jarosite can be used to investigate the potential of jarosite as a recorder of martian fluid-rock-atmospheric interactions, and as a K-Ar, U-Pb or Rb-Sr chronometer [6]. ToF-SIMS mapping of K, U, Pb, and Rb in MIL 03346 confirms the potential use of K-Ar in jarosite, but significant U, Pb or Rb was not de-tected (Fig. 2). U appears to correlate more with id-dingsite than with jarosite, and Rb with late-stage K-rich melt.

References: [1] Herd C. D. K. (2006) Meteoritics & Planet. Sci., 41, A74. [2] Fries et al. (2006) This volume. [3] Treiman A. H. (2005) Chemie der Erde 65:203-270. [4] Osawa T. et al. (2003) Meteoritics & Planet. Sci., 38, 1627-1640. [5] Mittlefehldt D. W. et al. (1997) Ant. Met. Research, 10, 109-124. [6] Papike J. J. et al. (2006) GCA, 70, 1309-1321.

Acknowledgements: Raman spectroscopy was carried out by Marc Fries (Geophysical Lab). I thank Anquang He (University of Alberta) for assistance with ToF-SIMS analysis. Funding was provided by Canadian Space Agency Contract 9F007-049417/001/ST to MDA Space Missions, as part of a Borehole Gamma Ray Spectrometer Concept Study.

Figure 1. (a) EMP X-ray ‘jarosite’ map (green) super-imposed on a BSE image, (b) Raman jarosite map, and ToF-SIMS maps of (c) K and (d) SO4

2- ions.

Figure 2. ToF-SIMS maps of Al, U, Pb and Rb, corre-sponding to the area shown in Figures 1c and 1d.

50 µm 10 µm

20 µm 20 µm

20 µm


Experimental Preservation of Amino Acids in Evaporitic Sulfate Minerals as Analogs for Surficial Processes on Mars. A.Johnson1 and L. M. Pratt2, 1Indiana University, Interdisciplinary Biochemistry Program, [email protected], 2Profesor of Geological Sciences, Indiana University, NASA Astrobiology Initiative: Bio-sustaining Life Cycles in the Deep Subsurface of Earth and Mars. 1001 E. 10th St. Bloomington, IN 47405-1405.

Introduction: As the exploration of our solar system expands and questions about possible environments that currently or previously harbored life arise, the necessity to have strategies for determining preservation potentials of biotic and abiotic organic molecules becomes imperative. Very little is known about the sequestration of these mole-cules as dissolved ions in fluid inclusions and interfacial water or sorbed in solid materials such as salt precipitates. The detection of sulfate mineral salts on the Martian surface by Viking and verification by MER data and orbital spectro-scopic instruments emphasizes the need to understand the preservation and possible catalytic activity of biologically relevant and detectable signatures in these environments. Therefore, a series of experiments is currently underway with preliminary work characterizing the distribution and sequestration of amino acids during diurnal cryo-evaporitic cycles under the low-pressure carbon dioxide atmosphere, radiation, and temperature found on the surface of Mars. We will focus directly on 1) effects of UV radiation on hydra-tion, dehydration, and solvation of amino acids in sulfate evaporites; 2) catalytic properties of sulfate minerals for potential polymerization; 3) crystal boundaries and fluid inclusions as sites for preservation of organic molecules; and 4) rates of amino acid racemization and degradation. Experimental: Micromolar amounts of glycine, L-alanine, L-valine, L-aspartic acid, and L-glutamic acid, rep-resentative of some 107 cells/mL of sample [1, 2] are sus-pended in end-member, carbon dioxide equilibrated brine solutions representative of the ion concentrations reported to exist in an aqueous environment in Martian regolith or bed-rock. These minerals include augite, anorthoclase, forsterite, ilmenite, pyrite and chlorapatite, as well as olivine-bearing basalts [3, 4]. Brines spend two to three weeks in a Martian simulation chamber exposed to a low- pressure carbon diox-ide atmosphere consistent with that suspected on Mars at a pressure of 10-15 mbar. Twelve-hour light and dark cycles with UV radiation from UV-C upward at a flux of 50 μEin-steins will imitate a Martian day cycle. Temperature end-points approach 9-10oC inside the chamber during the light hours and -80oC in the dark hours. This cyclic thawing, hydration and freezing of samples will provide insight into the role of water vapor and atmospheric interactions in the preservation of organic molecules. Samples will be removed and analyzed for mineral phase data using X-ray diffraction and amino acid characterization with gas chromatography, gas-chromatography mass spectroscopy, and high perform-ance liquid chromatography. Preliminary Results: Initial chromatographs indicate degradation of amino acids suspended in aqueous inorganic solutions under the Martian UV spectra at an intensity of 4.5 μEinsteins. Trace amounts of L-valine and L-alanine remain in solution, as well as numerous unidentified degradation products (Figure 1). In samples exposed to the diurnal tem-perature cycles only, and for those samples exposed to little

or no (<0.1 μEinsteins) terrestrial ultraviolet radiation, an unidentified product with retention times between 3.5 and 4 minutes appears in con-centrations greater than any of the individual amino acids alone (Figure 2). The retention time is less than L-glutamic and L-aspartic acids, indicating that glycine may be the pri-

mary reagent. The fluctua-tions in product retention times may be due to random polymerization of the product length. Mineral Analysis: Mineral

analysis of the evaporated samples by X-ray diffraction pro-vides interesting results on the crystal structure of the pre-cipitated brine salts. Samples were cryogenically evaporated in a low-pressure system to obtain suspected crystalline in-organic salts and organic residues. X-ray diffraction meas-urements made at room temperature and relative humidity near 35-38% showed no evidence for crystalline salts, both in the Mars brine analogs alone and in the Mars brine ana-logs laced with the amino acid mixture (Figure 3). The lack of simple crystalline salts upon evaporation implies that some mechanism prevented crystallization; this may be in part being due to the presence of the organic constituents and

experimental conditions. Conclusions: The pres-ence of unidentified product with retention times different than those of any of the initial amino acid standards indicates that low UV levels may play a role in the ran-

domization of amino acid hydrolysis products and act as an energy source for polymerization. The addition of brine solutions would seem to play little to no part in any preserva-tion mechanism for amino acids against UV radiolysis but may act as catalysts for the formation of random polymeriza-tion products. This could play an important role in subsur-face environments where regolith can block the majority of UV radiation. Subsurface environments on Mars may be characterized by large amounts of randomly polymerized organic matter, spurred by low temperature and low-level ultraviolet radiation. References: [1] Kminek, G., Bada, J.L. (2006). Earth & Planet. Sci., In Press.[2] Anton, J., Rossello-Mora. (2000) Appl. & Environ.Microbiology, 66, (7), 3052-3057. [3] Bullock, M.A., Moore. (2004) Icarus, 170, 404-423. [4] Tosca, N.J., McLennan, S.M. (2006). Earth & Planet. Sci., 241, 21-31.

Operations: Y Scale Add 35 | Import#5, NaMgSO4CO3Cl, 5 wk UV, 2-70/0.02, 23.6C, 35.8%RH, QTZ - File: Evaporite #5 5 wk UV.raw - Type: 2Th/Th locked - Start: 2.000 ° - End: 70.000 ° - Step: 0.020 ° - Step time: 6. s - Temp.: Operations: Import#2 powder, no organics, no UV, 23.0C, 38.5%RH, qtz - File: Evaporite #2, no organics, no uv.raw - Type: 2Th/Th locked - Start: 2.000 ° - End: 70.000 ° - Step: 0.020 ° - Step time: 2. s - Temp.: 2

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SULFUR SOLUBILITY IN MARTIAN MANTLE MELTS: IMPACTS ON THE LATE NOACHIANATMOSPHERE. S. S. Johnson1 , M. T. Zuber1, T. L. Grove1, and M. A. Mischna2, 1Department of Earth, Atmos-pheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 54-810, Cam-bridge, MA 02139; [email protected], 2Jet Propulsion Laboratory; 4800 Oak Grove Drive, M/S 183-401; Pasadena, CA91109, [email protected]

Introduction: Data recently returned from Marssuggest that sulfur may have played a significant rolein the planet’s evolution [1,2]. We present results froma model for sulfur delivery to the Martian surface witha special focus on the greenhouse warming effects ofH2S and SO2.

Sulfur Volatile Release: Volatile degassing asso-ciated with the formation of the Tharsis igneous prov-ince, a volume of 3x108 km3 thought to be largely em-placed by the end of the late Noachian [3], almost cer-tainly affected the early climate. As it remains unclearto what extent the more deeply intruded magma in theTharsis province communicated with the atmosphere,we explore the consequences of sulfur volatiles onclimate following large, discrete volcanic events.

Sulfur solubility: Using a batch melting model weobtain a high sulfur solubility in Martian silicate meltsin equilibrium with metal sulfide [4]. Because of theunique negative pressure dependence for sulfur solu-bility that dominates the positive temperature depend-ence in systems that contain FeO, sulfur from immisci-ble metal sulfide blebs will begin and continue to dis-solve directly into the silicate melt as soon as decom-pression melting commences. At the base of the litho-spheric lid, a final equilibration will take place beforethe liquid melt is advected to the planet’s surface.While significant cooling in passage through the crustcould affect the Sulfur Solubility Limit (SSL), here weassume that chemical and thermal halo effects insulatethe magma. In calculating the SSL in liquid silicateconditions, we use the formula:

ln SSL( ) = AT+ B + C

PT

⎛⎝⎜

⎞⎠⎟+ D ⋅nbo / t + lnaFeS

sulfide

SSL is in ppm, T in Kelvin, and P in bars [5]. ConstantsA, B, C and D are derived from a fit to experimentaldata [6]. nbo/t, the ratio of non-bridging oxygen anionsto tetrahedrally coordinated cations, is found usingAPXS compositional results from Gusev Crater basalts[7]. Petrology experiments on a Gusev basalt compo-sition document a three-phase multiple saturation of ol+ opx + spi near the liquidus at 10 kbars and 1583 K[8], giving rise to a sulfur solubility of ~1400 ppm.

Tharsis-radial dikes: We investigate two modelsfor the volume of lava thought to be rapidly emplacedby dike intrusions associated with Tharsis-radial gra-ben: a lower bound “Hanna Model,” 1500 km3 [9]; andan upper bound “Wilson Model,” 60,000 km3 [10].

Warming Results: For both H2S and SO2 end-members for the exsolved sulfur volatiles associatedwith these events, we find the additional greenhousewarming from absorption in wavelength windowscomplimentary to CO2. Using Mars-WRF , a three-dimensional GCM adapted for Martian conditions, weincorporate conservative model assumptions and afaint young Sun approximation (75% present-day lu-minosity) to investigate these sulfur volatile influxesinto both dry and H2O-saturated 50 mb and 500 mbbackground CO2 atmospheres. Results from annuallyaveraged surface temperatures indicate additional at-mospheric heating of 0-15 K from H2S pulses, 5-25 Kfrom SO2 pulses (Fig. 1), and localized conditions con-ducive to the presence of transient liquid water.

Conclusion: It appears that large, episodic releasesof sulfur volatiles early in Martian history may havecontributed to the generation of sufficient warming toaccord with the geologic evidence for near-surfaceliquid water. Photochemical modeling is underway todetermine the lifetime of these warming events.

Fig. 1: Additional SO2 warming in K, “WilsonModel” volatile pulse into a 500 mb CO2 atmosphere.

References: [1] Squyres, S.W. et al. (2004) Science,306, 1698-1703. [2] Gendrin, A. et al. (2005) Science,307, 1587-1591. [3] Phillips, R.J. et al. (2001) Science,291, 2587-2591. [4] Johnson, S.S. et al. (2006) LPSXXXVII Abstract #2094. [5] Holzheid, A. & Grove,T.L. (2002) American Mineralogist, 87, 227–237. [6]Mavrogenes, J.A. & O’Neill, H.St.C. (1999) Geo-chimica et Cosmochimica Acta, 63, 1173–1180. [7]McSween, H.Y. et al., (2006) JGR, 111, E02S19. [8]Monders, A.G. pers. comm. [9] Wilson, L. & Head, J.W. (2002) JGR, 107, 5057. [10] Hanna, J. pers. comm.


REVIEW OF RECENT THEORETICAL MODELS OF SALT SEQUENCES & SOLUTION COMPOSITIONS ON MARS P. L. King, Dept. Earth Sci., Univ. Western Ont., London ON N6A 5B7 Canada.

Introduction: A primary goal of missions to Mars

is to explore for extraterrestrial life and one way to focus such a search is to find evidence for water (solu-tions). It is necessary to use indirect clues to trace mar-tian solutions because water is not stable for extended periods of time under current surface conditions. Solu-tions that have dissolved and precipitated minerals may be evidenced by distinctive morphology, surface chemistry and mineralogy. Theoretical (thermody-namic and phase equilibria) approaches allow us to place constraints on the initial solution composition(s). From these starting compositions, we may predict equilibrium mineralogy of precipitates, evolution of solution compositions, environmental conditions, and variations locally and temporally on the martian sur-face.

Significant predictions from theoretical models: 1) Solutions on Mars are not like terrestrial seawater: To a first approximation, the surface of Mars is com-posed of mafic-ultramafic rocks and secondary miner-als (including salts and nanophase iron phases). Using this system, theoretical models assume that martian solutions are derived from fluids interacting with ma-fic-ultramafic rocks [1-6]. Resultant solutions are Mg-Na-(Ca-Fe)-SO4-Cl-rich and are unlike modern terres-trial seawater resulting in different geochemical path-ways [3, 5]. Mg-Na-(Ca-Fe)-SO4-Cl-rich solutions may be stable liquids on Mars' surface due to low eutectic temperatures (cf., Mg-SO4-H2O and Na-SO4-H2O systems [7]). These solutions may then be con-centrated (e.g., via evaporation or freezing) and upon removal of water and/or supersaturation of solutions, secondary minerals are formed. A sequence of salts may then be predicted [2-6] and compared with ob-served mineral assemblages and bulk compositions.

2) Solution compositions may vary with depth on Mars Mg-Na-SO4-Cl-rich salts dominate Mars' surface [review in 5] and carbonates have not been unambigu-ously identified on the martian surface [10], despite the CO2-bearing atmosphere [see 2, 5]. In contrast, the SNC (Shergottite-Nakhlite-Chassignite) meteorites, thought to come from Mars' subsurface, contain the sequentially crystallized salts: Ca-Mg-phosphate, Fe-Ca-Mg-carbonate, Ca-sulfate-(hydrate) through Na-Mg-(Ni)-sulfate, with minor chlorides and nitrates [8, 9]. The lack of carbonate at the surface, but occurrence in the subsurface with a distinctive salt sequence may be reproduced by theoretical models assuming that at different depths the solutions: a) are at different stages of evolution [5]; or, b) formed in distinctive geochemi-cal environments [11].

3) Environmental conditions may vary on Mars Salt sequences and solution compositions are signifi-cantly affected by pH, the partial pressure of CO2 and O2, and the activity of sulfur compounds [1-5, 11-18]. Of these variables, the treatment of pH is one of the major differences between models, with some authors emphasizing acidic conditions in a "recent" acid fog model [6, 12, 13] and others allowing pH to vary via leaching models [2, 4, 5, 11]. In recent acid fog mod-els, Fe and Al are held in solution [12] and carbonates are destroyed [14, 15]. In variable pH models, the so-lutions evolve to high pH conditions [4, 11], and at neutral to basic conditions Fe phases (e.g., hematite or siderite) precipitate, depleting the solution in Fe.

Challenges in theoretical modeling: 1) Most thermodynamic models use data at standard tempera-ture and pressure which is adequate, but data at mar-tian conditions may be more appropriate [16]. 2) Thermodynamic models do not consider reaction ki-netics which may be significant on Mars, particularly for Fe-bearing phases [14]. 3) Reactions may be ob-scured by open system processes such as, episodic aqueous events and varying water:rock ratios [17]; Si-rich coatings [4]; and physical processes that may dis-turb mineral assemblages (e.g., dust storms & impact events). 4) There are few unique solutions for the for-mation of surface mineral assemblages on Mars. For example, in the Columbia Hills the rocks may form by adding minerals, weathering at neutral-basic or acidic conditions, or adding a primitive to evolved brine [18]. To distinguish between different hypotheses it is nec-essary to examine textural evidence for the salt pre-cipitation sequence in situ on the martian surface [18]. References: [1] Burns, R. G. (1988) LPS XVIII, 713. [2] Catling, D. C. (1999) JGR 104, 16453. [3] King, P. L. et al. (2001) Goldschmidt Conf. 11, 3612. [4] King, P. L. & McSween, H. Y. (2005) JGR 110, doi:10.1029/2005JE002482. [5] King, P. L. et al. (2004) GCA 68, 4993. [6] Tosca, N. J. et al. (2004) JGR 109, doi:10.1029/2003JE002218. [7] Brass, G. W. (1980) Icarus 42, 20. [8] Bridges J. C. et al. (2001) Space Sci. Rev. 96, 365. [9] McSween, H. Y. & Treiman, A.H. (1998) Rev. Mineral. 36, Ch. 6. [10] Stockstill K. R. et al. (2005) J. Geophys. Res. 110, doi:10.1029/2004JE002353. [11] Tosca, N. J. & McLennan, S. M. (2006) EPSL 241, 21. [12] Hurowitz J. A. et al., (2005) JGR 111, doi:10.1029/2005JE002515. [13] Tosca N. J. et al. (2005) EPSL 240, 125 (2005). [14] Burns, R. G. & Fisher, D. S. (1993) JGR 98, 3365. [15] Fairén, A. B. et al. (2004) Na-ture 431, 423. [16] Marion, G. M. et al. (2003) GCA 67, 4251. [17] Elwood Madden, M. E. et al. (2004) Nature 431, 821. [18] King, P.L. & McSween, H. Y. (2006) LPSC XXXVII, 2108.


SULFATES AND OTHER SALTS ON THE MARTIAN SURFACE HAVE THEIR SOURCE DEEP IN THE CRUST. G. G. Kochemasov, IGEM of the Russian Academy of Sciences, 35 Staromonetny, 119017 Moscow, Russia, [email protected] Sulfate crusts (Opportunity) [1-7 and others] and crumbly covers on rocks (Spirit) are hypergene in origin. They have to have a sulfur source in igneous rocks either on surface (Spirit) or deep in the highland crust (Opportunity). The alkaline thinly layered rocks at Columbia Hills are rather rich in sulfur, chlorine, bromine (maybe, fluorine that cannot be detected by APXS), thus the source of anions for light (white) mainly sulfate minerals discovered under thin reddish eolian deposits is more or less clear. Cations are Mg, Fe, Ca –elements also abundant in underlying rocks. Na and K also form secondary minerals but they are not so widespread because they are probably more easily leached under martian varied moisture conditions. (Veneers of Na and Fe sulfites-thenardite, rozenite, melanterite- are known on fresh blocks of excavated agpaites and miascites at Lovozero and Khibiny alkaline massifs, Kola Peninsula). On Opportunity Planum the flatly lying eolian Burns formation [4, 7] is densely “peppered” with white spots representing salt depositions(mainly sulfates) around and inside of craters of various sizes. Some planetologists see in them traces of impacts but an unprejudiced sight at the image below {PIA05485, MOC image of MGS, Meridiani Plains] shows that the “holes’ with white halos prefer to follow a few intersecting directions (N-S, NW, NE, W-E) and thus reflect well known in planetology system of cracks (faults) developed in rotating bodies. Some holes, nevertheless, could be impacts. In any case these holes –real channels into underlying depths give way to surface for crustal hydrothermal solutions. These solutions rich in S, Cl, Br, K, Na, Mg, Ca, Fe (the last three elements can be taken from crossed basic sills or covers) penetrate not very compact eolian sandy deposits and weathered rocks and cement them by salts (mainly by sulfates). Some salts can be deposited in small temporary inter-dune and crater “lakes” formed by excessive outpourings. Further eolian activity during eons can break these salty deposits and redeposit them in form of sandy fragments mixed with eolian and more large rock fragments. But where lies a source of these solutions so rich in metals, alkalis, volatiles ? Most probably deep in the crust . What kind of igneous lithologies composes the continental martian crust? There are a few constraints for its composition. First of all, it must be built of light not dense material to explain nearly even gravity over the whole martian surface. Then, it has to be rich in water or constitutional water to explain sporadic hugh outpourings of

liquids onto surface producing large and small gullies and valleys. Then, it has to be rich in other volatiles and alkalis, particularly in S, Cl, Br, Na, K, possibly F. Obviously, basalts are not fit for these constraints. Earlier [8 and others] we proposed the light not dense crust composed of alkalic rocks like syenites, albitites and granites. Now nepheline-normative rocks and alkali basalts are found at Columbia Hills [9-12] –an outlier of highland rocks. Perfectly fit for above constraints low density feldspathoids like sodalite (hackmanite) and nosean, rich in S, Cl, and normally associated with them zeolites {OH) [13]. Containing them rocks –foidites

thus have the constitutional water and hidden in feldspathoids salts. It is very probable that martian foidites contain also free salts as these low density substances diminish an overall rock density what is necessary for building very high standing martian southern highlands. The highlands can include dykes and sills of basic rocks and large layered basic massifs like Bushveld in Africa and covered by plateau-basalts (Meridiani Planum?). Signs of basic rocks are seen by the instruments of MGS, Odyssey, MER (Fe, Mg, olivine, pyroxenes are easily detectable). References: [1] Squyres S.W., Arvidson R.E., Bell III J.F. et al (2004) Science, v. 306, # 5702, 1698-1703; [2] Rieder R., Gellert R., Anderson R.C. et al. (2004) Ibid.,1746-1749; [3]Christensen P.R., Wyatt M.B., Glotch T.D. et al. (2004) Ibid., 1733-1739; [4] Squyres S.W., Knoll A.H. (2005) Earth & Planetary Science Letters, v. 240, Issue 1, 1-10; [5] Clark B.C., Morris R.V., McLennan S.M. et al. (20050 Ibid., 73-94; [6] Tosca N.J., McLennan S.M., Clark B.C. et al. (2005) Ibid., 122-148; [7] Grotzinger J.P., Arvidson R.E., Bell III J.F. et al. (2005) Ibid., 11-72; [8] Kochemasov G. G. (1995) Golombek M.P., Edgett K.S., Rice J.W. Jr. (Eds). Mars Pathfinder Landing Site Workshop II: Characteristics of the Ares Vallis Region and Field trips to the Channeled Scabland, Washington. LPI Tech. Rpt. 95-01. Pt.1.LPI, Houston, 1995, 63 pp.; [9] Gellert R., Rieder R. Bruckner J. et al. (2006) JGR Planets, v.111, #E2, E02S05; [10] Ming D.W., Mittlefehldt D.W., Morris R.V. et al. (2006) Ibid., E02S12; [11] Squyres S.W., Arvidson R.E., Blaney D.L. et al (2006) Ibid.,E02S11; [12] McSween H.Y. et al. (2006) JGR Planets, submitted; [13] Kochemasov G.G.(2006)(abs.), posted Feb. 2006 in a Workshop on Martian Water: Surface and Subsurface, NASA Ames Research Center, Moffett Field, California, Febr. 23-24, 2006 at http://es.ucsc.edu/~fnimmo/website/mars2006.html, <http://es.ucsc.edu/%7Efnimmo/website/mars2006.html>.


DISSOLVED SULFATE ANALYSIS ON THE 2007 PHOENIX MARS SCOUT MISSION. S. P. Kounaves, S. M. M. Young, J. A. M. Kapit, and The Phoenix Team, In-Situ Planetary Chemical Analysis Lab, Department of Chemistry, Tufts University, Medford, MA 02155 USA.

Introduction: Sulfate is of paramount importance

in understanding both Mars’ geochemistry and its abil-ity to support past or present microbial life. Elemental sulfur has been detected on Mars using a variety of X-ray methods, both in situ by Viking [1], Pathfinder [2], and the two MERs [3,4], and most recently from orbit by OMEGA [5]. From the returned data it has been hypothesized that that the predominated form of sulfur is sulfate. These X-ray methods though are not able to resolve whether sulfur exists in its elemental form or as sulfide, sulfate, sulfite, or any other form. Thus, it is important to ground truth the existence of sulfate and also determine which cations are associated with the it. Carrying out such wet chemical analyses on Mars is challenging and no landed mission to date has attempted to determine soluble ionic species in the Martian regolith.

The Wet Chemistry Lab: The 2007 Phoenix in-cludes, as part of the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA), four Wet Chemis-try Labs (WCL) [6]. Each WCL is composed of an upper and lower assembly. The lower “beaker” con-

sists of an array of sensors for meas-uring pH, Eh, con-ductivity, redox species via cyclic voltammetry, hal-ides via chronopo-tentiometry, heavy metals via anodic stripping voltam-metry, and dis-solved ions via ion selective electrodes (ISE). The ionic

species to be determined include Ca2+, Mg2+, K+, Na+, NH4

+, Cl-, Br-, I-, NO3-, and SO4

=. The upper assembly consists of a leaching solution reservoir (water and the first calibrants for the sensors), a 1cc sample drawer, and a reagent dispenser that holds five crucibles, in-cluding one for a second calibrant, another for an acid, and three with barium chloride for determination of sulfate.

During the first sol, the analysis consists of the WCL receiving a sample of regolith (soil) from the robotic arm, adding the initial leaching solution, taking data, adding a second calibrant, taking data, then add-ing the soil sample. After equilibration and data collec-tion, the sample will freeze overnight. On the second

sol, the acid will be added, data collected and then the sulfate will be determined.

Sulfate Analysis: Design and fabrication of the WCL posed many challenges, but the lack of a viable sulfate specific sensor introduced even greater compli-cations. While a couple of sulfate ISEs have been de-scribed in the literature, their responses in solutions other than where all anions are either absent or chemi-cally or physically removed, have been dismal. Thus, it would be difficult to obtain a reliable sulfate analysis of a regolith sample with such sensors.

The WCL overcomes this analytical problem by exploiting the fact that, even under acidic or basic con-ditions, barium and sulfate form an insoluble precipi-tate of barium sulfate. Thus, following the extensive analyses of the leached regolith sample, the final phase of the analysis will determine sulfate via a barium ti-tration using the Ba2+ ISE. Via the last three crucibles, measured amounts of BaCl will be added to the sam-ple. The Ba2+ will react with any dissolved SO4

= and precipitate as BaSO4. The Ba2+ sensor will measure the barium remaining in solution, and by simple sub-traction, provide how much precipitated with the sul-fate, i.e. how much sulfate was present. With respect to the 1 gram sample of Mars regolith, the first barium addition can precipitate up to 6% sulfate, the second addition extends the measurement to 12%, and the third to about 18%.

In preparation for the Phoenix mission, we are cur-rently characterizing all the sensors, including the complete electroanalytical method for determining sulfate via the barium standard subtraction method using the Ba2+ ISE. Characterization will include a variety of standard solutions, geological Earth sam-ples, Mars simulants, and sawdust from the EETA790001 Martian meteorite. We will be deter-mining a variety of Ba2+ sensor response characteris-tics such as the limits of detection, interferences, and other constraints imposed by the Martian environ-mental conditions. In addition, we will also develop a response library to aid in the interpretation of the data.

References: [1] Clark B. C. et al. (1982) JGR, 87, 10,059-10,067. [2] Rieder R. et al. (1997) Science, 278, 1771-1774. [3] Gallert R. (2004) Science, 305, 1829-832. [4] Rieder R. et al. (2004) Science, 306, 1746-1749. [5] Langevin Y. (2005) Science, 307, 1584-1586. [6] Kounaves S. P. et al. (2003) JGR, 108, 5077-5088.


Active and Noble Gas in Terrestrial Jarosite- and Alunite-Hosted Fluid Inclusions: Insights and Constraints on Formation of Martian Sulfates. G. P. Landis1 and R. O. Rye1, 1U.S. Geological Survey, P.O.Box 25046, Mail Stop 963, Denver Federal Center, Denver, CO 80227, [email protected] and [email protected].

Introduction: Terrestrial alunite and jarosite crys-

tals contain fluid inclusions which retain the active and noble gas compositions of parent fluids. Data on these fluids provide critical clues to the geochemical envi-ronment of their formation. Jarosite has been recog-nized on Mars (alunite, the K-Al analog of jarosite, likely is present as well). Thus, jarosite (and alunite) can be viewed as fluid ‘sampling devices’ in planning future Martian exploration and sampling strategies. Fluid inclusions potentially ‘record’ the volatile com-position of sulfate-forming parent fluids. When cou-pled with stable isotope geochemistry and argon geo-chronology ages, data on these fluids can be inter-preted in terms of their source(s) and evolution from deep origins and modifications with ascent into the near-surface to surface environments during sulfate formation, and over billions of years of exposure to Martian hydrosphere and atmosphere .

Fluid Inclusions and Diffusion: Active (N2, CH4, CO, CO2, H2, O2, HF, HCl, H2S, SO2, and light chain hydrocarbons) and noble (He, Ne, Ar) gases have been detected in micron-sized inclusions [1] of fluid (aque-ous liquids to low-density vapor-gas) that were trapped in alunite during formation (figure 1).

Figure 1. (Left) Magmatic Steam alunite, Cactus, NV. Vapor-

dominate 0.9 µm elongate fluid inclusion with 0.2 µm hematite nuclei. (Right) Two-phase liquid-gas inclusion, El Indio, Chile alunite. Prominent 0.16 mm inclusion and 0.09 mm gas bubble and adjacent low-density vapor inclusions.

Step heating experiments on alunite yield diffusion

log D0 (cm2/sec) and E (kJ mol-1) for (3He) = -7.85 and 40.2, for (4He) = -4.33 and 106.8, and for (40Ar) = 2.45 and 225. Model 1/e-folding times and diffusion dis-tance-time calculations indicate helium and argon re-main in alunite at ≤ 100°C and < 200-220°C respec-tively. In part, this explains the success of argon geo-chronology using alunite and jarosite. Diffusion data support the anecdotal arguments that, in the absence of later thermal or metamorphic deformation of alunite and jarosite, volatiles in fluid inclusions are retained in

these minerals as quantitative samples of the parent fluids. The original volatile chemistry of parent fluids was preserved for 1.87 Ga in fluid inclusions in alunite from the Brazilian Tapajós gold deposit [2].

Alunite and Jarosite Environments: Terrestrial alunite forms in deeper high temperature magmatic hydrothermal environments, in near-surface high tem-perature magmatic steam, and (along with jarosite) in steam-heated environments and in surficial low tem-perature supergene environment including lacustrine analogs. Alunite and jarosite form from high sulfur, high oxidation-state, low pH, aqueous solutions that range from low-density steam (volatile) fluids as high as 400°C to low temperature surface waters. The envi-ronment of origin will be reflected in different gas compositions of fluid inclusions and isotopic composi-tions of host minerals. Crystal growth bands (figure 2) may reflect influence of pulsing of magmas whose fluids have variable volatile and isotopic chemistry. The environment of origin of these sulfate minerals are reflected in the sulfur (H2S/SO2) and carbon (CH4/CO2) gas speciation, abundance of HF, Cl, and H2, and helium, neon, and argon isotopes. In high tem-perature environments only partial equilibrium is ob-served among active gas components in fluid inclu-sions [1]. In supergene environments, atmospheric gas in solubility-limited amounts is observed in fluid inclu-sions. Martian jarosite is likely to contain fluid inclu-sions whose active and rare gas chemistry can advance our understanding of magmatic volatile processes, pro-vide insights into precipitation mechanisms, trace are-ologic atmosphere and hydrosphere evolution, and possibly detect biotic organic material (amino acids or fragments) as evidence for life.

Figure 2. Deposition Bands in alunite (left-Alunite Ridge, Utah)

and jarosite (right-Gilbert, Nevada). References: [1] Landis G. P. and Rye R. O. (2005)

Chem.Geol., 215, 155-184. [2] Landis G. P., Snee L. W., and Juliani C. (2005) Chem.Geol., 215, 127-153.


DETERMINING THE CHEMISTRY OF THE BRIGHT PASO ROBLES SOILS ON MARS USING MULTISPECTRAL DATA SETS. M. D. Lane1, J. L. Bishop2, M. Parente3, M. D. Dyar4, P. L. King5, and E. Cloutis6. 1Planetary Science Institute, Tucson, AZ ([email protected]), 2SETI Institute/NASA-Ames Research Center, Mountain View, CA, 3Stanford University, Stanford, CA, 4Mount Holyoke College, South Hadley, MA, 5Univ. of Western Ontario, Canada, 6Univ. of Winnipeg, Canada.

Introduction: The Mars Exploration Rover

(MER) in Gusev Crater has exposed in its tracks an unusual occurrence of a soil high in sulfur and high in phosphorus [1-3] at a site called Paso Robles. This salty soil is thought to be composed of the following: Fe3+-, Mg-, and Ca-sulfates; Ca-phosphate; hematite, halite, allophane, and amorphous Si [1]. We are cur-rently studying a large suite of sulfate minerals [e.g., 4-8] using a variety of methods including midinfrared emission, reflectance, and micro-transmission spectro-scopies, plus visible-near infrared (VNIR) spectros-copy and Mössbauer (MB) spectroscopy. Included in our sulfate studies are numerous Fe3+ sulfates that are clearly an important mineral phase of the anomalous Paso Robles soils. Hence, we are applying our spec-tral databases to the interpretation of various MER datasets to further explore and better understand the chemistry of these salt-rich soils. The focus of this work is to attempt to identify the sulfate chemistry of the Paso Robles soils using a unified application of emissivity, VNIR, and Mössbauer spectroscopy.

Emissivity Spectra: The soil exposed in the MER tracks is typically dark, and the bright soil at Paso Robles that contains ~32% sulfate [1] is fairly rare, but has been found in more than one location (e.g., also at Arad and Tyrone). Miniature Thermal Emission Spec-trometer (Mini-TES) [9] data of rover track soils that are dark (from sols 400 and 403) and bright (sol 404) were studied. Spectral deconvolution of the bright-soil spectrum was conducted using an endmember array that included the dark-track soil as well as common rock-forming minerals and a diverse suite of sulfates.

Fig. 1: Mini-TES spectra of bright and dark track soils and the modeled fit to the bright spectrum.

The deconvolution result (Fig. 1) achieved an RMS of 0.064%. The result showed the bright soil spectrum to be dominated by ~49% dark-track soil; plus ~13% kornelite (Fe2(SO4)3·7H2O) (XRD pending) , ~13% yavapaiite (KFe(SO4)2), and ~7% metahohmannite (Fe2(SO4)2O·4H2O) (XRD pending) [all ferric sul-fates]. APXS data [3] show the Paso Robles soils to be depleted in K; however, omitting the K-bearing yavapaiite from the allowed endmembers severely degrades the deconvolution fits. At or below the ca-nonical “5% detection limit” were leonite (~5%), ferri-copiapite (~3%), and a smattering of other minerals, including apatite (Ca-phosphate) at 0.2%. However, the identifications of these minor mineralogies may be inaccurate.

VNIR Spectra: Clustering via statistical analyses of the data from the Panoramic Camera (Pancam) [10] scenes of Paso Robles’ tracks provided “typical” and “anomalous” spectra. The anomalous spectra occurred in the bright regions of the images. These spectra ex-hibited diagnostic spectral characteristics (e.g., reflec-tance maximum at ~670 nm, a minimum near 800-850 cm, and a convex upward feature near 480 nm) that are indicators of the possible presence of coquimbite, kor-nelite, copiapite, fibroferrite, and yavapaiite mixed with darker soil constituents. These identified sulfates are all ferric-bearing minerals.

Mössbauer Spectra: Paso Robles MB spectra were processed using MERView [11]. An extensive suite of sulfates have been compared to the data and likely mineral candidates have been identified, includ-ing Fe (III) sulfates. Details are forthcoming.

Results: On the basis of our results to date. We believe the sulfates of the anomalous bright soil ex-posed in the tracks at Paso Robles are dominated by coquimbite/kornelite (and perhaps yavapaiite) with other ferric sulfates possibly being present.

Acknowledgments: This work is supported by NASA’s MFR and Mars Odyssey PS Programs.

References: [1] Ming, D. W. et al. (2006) JGR, 111, E02S12. [2] Arvidson, R. E. et al. (2006) JGR, 111, E02S01. [3] Gellert, R. et al. (2006) JGR, 111, E02S05. [4] Lane, M. D., Am. Miner., ac-cepted. [5] Dyar, M. D. et al. (2005) LPS XXXVI, abs. 1622. [6] Lane, M. D. et al. (2005) LPS XXXVI, abs. 1442. [7] Bishop, J. L. et al. (2005) Int’l J. Astrobiol., 3(4), 275-285. [8] King, P. L. et al. (2005) 5th Can. Space Expl. Wksp, abs. SE0539. [9] Christensen, P. R. et al. (2003) JGR, 108, 8064. [10] Bell, J. F. et al. (2006) JGR, 111, E02S03. [11] Agresti D. et al. (2006) LPS XXXVII, abs. 1517.


RADIOLYTIC OXIDATION OF PYRITE: A VIABLE MECHANISM FOR SULFATE PRODUCTION ON MARS? L. Lefticariu1, L. M. Pratt1, J. A. LaVerne2, E.M. Ripley1, 1Department of Geological Sciences, Indiana University, 1001 E 10th St., Bloomington, IN 47405, ([email protected]), 2 Radiation Laboratory, University of Notre Dame, Notre Dame, IN 47405.

Introduction: Passage of ionizing radiation

through water produces a complex mixture of short-lived ions, free radicals, and electronically excited molecules that can participate in a wide range of chemical reactions involving solutes and solids [1], [2]. In groundwaters associated with U deposits, reac-tions between radiolytically produced radicals and aqueous or solid media result in complex mixtures of oxidized and reduced products that can accelerate wa-ter-rock interaction [3]. In subsurface environments, radiolysis of water coupled to oxidation of sulfide min-erals can produce gradients of both electron acceptors and electron donors that are possible sources of meta-bolic energy [4].

Recent data from Mars Exploration Rovers provide multiple lines of evidence indicating the extensive presence of sulfates on Mar’s surface and possible subsurface [5], [6], [7]. Measurements by NASA’s Mars Pathfinder and Viking landers showed that sulfur is a substantial component of soil dust and surface rocks [8]. Evidence of hydrated sulfate salt deposits in the Martian tropics comes from near-infrared spectral data on Mars Express [9], [10]. In addition, sulfates have been identified in SNC meteorites, which contain salt minerals including sulfates, up to 1% by volume. These evidences taken together strongly suggest that sulfate minerals are on the Mars surface and within the upper lithosphere. Sulfate minerals are a potential archive of information on both the sulfur geochemical cycle and history of water on Mars.

Traditional models for the oxidation of sulfide min-erals in aerobic environments involve the presence of O2 and H2O, as the key oxidants for sulfides. In recent years, however, geochemists have increasingly recog-nized that radiolysis could be an effective process in producing active oxidizing species on Mars and can play a pivotal role as a source of oxidants in deep va-dose zones.

Experimental Methods: In order to evaluate the efficiency of radiolytic sulfide oxidation in the produc-tion of sulfate gradients and the stable isotope ratios of sulfur products, we performed a series of radiation experiments using pyrite and deionized water. Radia-tion experiments were carried out at room temperature using a a 60Co gamma source at the Radiation Labora-tory of the University of Notre Dame. The dose rate was of 11.3 krad/min (113 Gy/min), as determined by the Fricke dosimeter. The total dose was from 0.3 to 1.5 x 104 Gy. Water used was de-oxygenated to mini-

mize competing reactions with O2. The water/pyrite mixtures were degassed and flame sealed in 2 cm outer diameter, 10 cm long quartz tubes. After irradiation, the gaseous, aqueous, and solid species produced dur-ing radiolysis were collected, quantified, identified, and measured.

Results and Discussion: Radiolysis of pyrite in the presence of water is characterized by a complex interplay between different radicals and oxidants to-wards producing sulfate. Molecular hydrogen was the dominant gas collected at the end of pyrite-water irra-diation experiment. Sulfate was the only aqueous sul-fur species detected by ion chromatography. The yield of aqueous sulfate and molecular hydrogen in experi-ments in which we used pure deoxygenated water and pyrite correlates with the total irradiation dose. Our ongoing studies are probing the overall chemistry in-volved in radiolysis of H2O/FeS2 and aim to identify possible intermediate species between pyrite and the end-product SO4

2-. We will also examine effects of pH and different additives (e.g., H2O2, O2, CO2) in terms of aqueous sulfate speciation and aqueous sulfate yields under different experimental conditions.

Our results indicate that radiolysis is an efficient mechanism for producing oxidizing species that can oxidize pyrite in contact with water.

Conclusions: Recognition that crustal radiolysis is an efficient mechanism in the production of oxidizing species in geologically long-lived oxidizing systems has profound implications for assessing microbial me-tabolism in the deep subsurface on Earth and Mars. Radiolytic processes are effective in producing hydro-gen and sulfate gradients even in water-limited envi-ronments, such as predicted for Mars. References: [1] Garrett B. C. et al., 2004, Chem. Rev., 105, 355-390. [2] Pastina B., and LaVerne, J.A., 20001, J. Phys. Chem., 105, 9316-9321. [3] Fayek, M., et al., 1997, Appl. Geochem. 12, 549–565. [4] Indiana Princeton Tennessee Astrobiology Initia-tive: http://www.indiana.edu/~deeplife/research.html. [5] Gedrin et al., 2005, Science 307, 1587-1591. [6] Langevin et al., 2005, Science 307, 1584-1586. [7] Bibring et al., 2005, Science 307, 1576-1581. [8] Squyres et al, 2004, Science, 306,1698-1703. [9] En-crenaz at al, 2004, Icarus 170, 424–429. [10] Clancy et al., 2004, Icarus 168, 116–121.


SULFATES AS GEOCHRONOMETERS/GEODOSIMETERS FOR IN-SITU MARS SURFACE SCIENCE. K. Lepper, T. Morken, and A. Podoll, Optical Dating and Dosimetry Lab, Department of Geosciences, North Dakota State University, 218 Stevens Hall, Fargo, ND, 58105 ([email protected]; [email protected]; [email protected])

Introduction: Sulfate mineral deposits on the sur-

face of Mars are a potential storehouse of data record-ing the evolution of Mars’ surface environment and climate. However, one of the greatest challenges to deciphering these types of martian geo-records will be the need for absolute dating techniques, particularly those techniques applicable to the timeframes of Mars surface processes [1]. Lepper and McKeever [2-4] have proposed developing optical dating, an estab-lished terrestrial chronometric dating method based on principles of solid-state physics, for remote in-situ dat-ing of martian silicate sediments.

In addition to silicates, sulfate salts also exhibit ra-diation induced, stimulated anti-stokes luminescence that can have dosimetric and geochronologic signifi-cance. However, because these salts are chemically unstable in a vast majority of Earth surface environ-ments, their optical dating properties have been largely unexplored. We report here preliminary results of on-going experiments with magnesium and sodium sulfate salts as well as review past work with calcium sulfate salts, to assess the radiation dosimetric and geochro-nologic properties of these minerals. The goals of our current phase of experimental work are to: (i) evaluate the influence of accessory concentrations of sulfates in Mars surface deposits on optical dating of silicate min-erals, (ii) identify potential martian indigenous geodo-simeters, (iii) and evaluate the plausibility of using sulfates as primary in-situ geochronometers on Mars.

Methodological Background: Over geologic time, ionizing radiation from the decay of naturally occurring radioisotopes and from cosmic rays liberates charge carriers (electrons and holes) within mineral grains. The charge carriers can subsequently become localized at crystal defects leading to accumulation of a “trapped” electron population. Recombination of the charge carriers and relaxation results in photon emis-sion, i.e. luminescence. The intensity of luminescence produced is proportional to the amount of trapped charge, and thereby to the radiation dose absorbed by the mineral grains since deposition at the sampled site. A determination of the ionizing radiation dose rate at the sample location allows the age of the deposit to be determined (from Age = Absorbed Dose / Dose Rate). Experimentally, optical excitaion is used to initiate the measurement process which gives rise to the method’s name - optically stimulated luminescence (OSL) dating or, simply, optical dating.

Synopsis of Experimental Results: Calcium Sulfates. Synthetically grown CaSO4

doped with Mn, Dy, or Tm form a family of highly sensitive thermoluminescent dosimetric materials [5] that exhibit much greater radiation sensitivity and sig-nal reproducibility than natural calcium sulfates. Re-cently, Singhvi and student [6] have directly dated gypsum (CaSO4•2H2O) sand dunes at White Sands, New Mexico with OSL methods, but found small amounts of quartz incorporated in the dunes to give more precise results than measurements made on the gypsum grains. Although developmental work may be needed, it appears that calcium sulfates may have the potential to serve as OSL geochronometers on Mars.

Sodium Sulfates. The dosimetric properties of doped Na2SO4 have also been widely examined. Our measurements of unannealed dopant-free thenardite (Na2SO4) indicated UV phosphorescence following beta irradiation and both infrared and blue stimulated UV luminescence. However, none of these lumines-cence signals were stable over short time scales suggesting that natural unheated thenardite is an unlikely candidate for an in-situ martian geochro-nometer. We have observed that annealing can induce complex dosimetric behaviors in thenardite linked to structural phase changes [7], which may hold the potential for in-situ geodosimetry.

Magnesium Sulfates. We have also carried out pre-liminary optical dating characterizations on Kieserite (MgSO4•1H2O) and Hexahydrite (MgSO4•6H2O). These magnesium sulfates did not exhibit phosphores-cence or infrared stimulated luminescence. However, they did show blue stimulated luminescence with much greater dosimetric stability than thenardite and shared certain geochronometric characteristics with both quartz and feldspars. More detailed examinations of magnesium sulfates are warranted.

References: [1] Clifford S.M. et al. (2000) Icarus, 144, 210-242. [2] Lepper K. and McKeever S.W.S. (1998) LPI Contribution No. 953. [3] Lepper K. and McKeever S.W.S. (2000) Icarus. 144, 295-301. [4] McKeever, et al. (2003) Radiat. Meas. 37, 527-534. [5] McKeever, S.W.S. (1985) Thermoluminescence of solids. Cambridge Univ. Press. [6] Singhvi, A. (2006) 4th NWLDDW, Abst. Vol. VI: 22. [7] Chio, B. and Lockwood, D. (2005) J. Phys. Cond. Mat. 17:6095-6108.


TEXTURAL AND STABLE ISOTOPE DISCRIMINATION OF HYPOGENE AND SUPERGENE JAROSITE AND ENVIRONMENT OF FORMATION EFFECTS ON 40AR/39AR GEOCHRONOLOGY. V. W. Lueth, New Mexico Bureau of Geology & Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801, [email protected]

Introduction: Jarosite has been shown to form in a

multitude of environments ranging from hydrothermal conditions [1] to surface weathering [2]. Mineral tex-tures and associations, coupled with stable isotope analysis, have proven invaluable in differentiating be-tween these environments of formation. Additionally, 40Ar/39Ar spectra reflect differences in environments of formation. These techniques will be essential in char-acterizing jarosite, or other acid sulfate minerals, from the Martian surface.

Textures and Associations: Specific mineral tex-tures, associations, and paragenetic sequences appear consistent between environments.

Supergene. Jarosite is finely crystalline with the largest crystallites up to approximately 1mm. It is of-ten intermixed with hypogene phases, especially clays. Jarosite is early in the supergene paragenesis and al-tered to goethite/hematite with subsequent weathering; often destroyed unless fortuitously preserved.

Hypogene. Large crystals (up to 3 cm) of high pu-rity (but highly zoned) characterize hypogene jarosite occurrences. Impurities encountered in these samples are typically other ore/gangue minerals. The mineral paragenesis is opposite that of supergene environments where hematite and gypsum are typically replaced by jarosite late in the sequence.

Stable Isotopes: The chemistry and structure of jarosite allow for reliable age dating and the determi-nation of the stable isotope values of sulfur, hydrogen and oxygen in both the SO4 and OH sites. Sulfur iso-topes encode the origin of the sulfur whether from preexisting sulfide (supergene) or oxidation of sulfur gases (hypogene). Hydrogen reflects the origin of the water at the time of formation. Oxygen in the SO4 site reflects the source of oxygen during oxidation and coupled with OH values, that reflect the character of the water, can be used as a geothermometer.

Comparison of supergene and hypogene jarosite of similar ages illustrates how stable isotopes discrimi-nate between supergene and hypogene jarosite (Fig. 1).

40Ar/39Ar Geochronology: Analytical spectra dis-play significant differences, depending on the origin of the jarosite (Figure 2). The small crystal sizes and in-corporation of other minerals results in less than opti-mal age spectra for supergene jarosite. Poor crystallin-ity, recoil, Ar loss, and contamination are endemic to supergene samples. Sophisticated separation tech-niques and chemical treatments are required to obtain

reliable results. Samples from the surface of Mars will probably require difficult separation techniques to pro-duce reliable age dates.

Figure 1. Hydrogen and SO4-oxygen plot. SJSF = su-pergene jarosite field of [2].

Figure 2. Comparison of Ar spectra for supergene (top) and hypogene (bottom) jarosite.

References: [1] Lueth, V.W., Rye, R.O., and Pe-ters, L., (2005) Chem. Geol., 215, 339-360. [2] Rye, R.O. and Alpers, C.N., 1997, USGS OFR 97-88.


EVOLVED GAS ANALYSIS ON THE 2009 MARS SCIENCE LABORATORY. P. R. Mahaffy1 and H. B. Franz2, 1NASA Goddard Space Flight Center, Code 699, Greenbelt, MD 20771 ([email protected]), 2Department of Geology, University of Maryland, College Park, MD 20742 ([email protected]).

Introduction: Sulfates on Mars have been directly

studied or inferred from a variety of experiments. These include the in situ Viking Lander XRS experi-ments [1] and laboratory chemical analyses of martian meteorites [2, 3]. Mars Pathfinder [4] and more re-cently the MER rovers have measured sulfur with the alpha particle backscatter experiment. The sulfate-containing rocks at Meridiani [5] have been found to contain the mineral jarosite, which can be uniquely identified with the Mossbauer instrument. The identifi-cation of jarosite at Meridiani was one of the early indicators of aqueous processes at that site [6]. Various Fe, Ca, and Mg sulfates have also been identified in the rocks of Columbia Hills [7], with varying degrees of aqueous alteration inferred in several different rock classes. Recent maps of hydrated and sulfate mineral distributions on Mars have been obtained from the Mars Express OMEGA experiment [8], and these to-gether with additional data expected soon from the Mars Reconnaissance Orbiter will significantly en-hance the site selection process for future surface landers, for either in situ exploration or sample return.

The 2009 Mars Science Laboratory (MSL) [9] is designed to greatly expand our ability to identify min-erals on Mars as well as associated organic or inor-ganic volatiles. Samples screened by MSL remote sensing and contact instruments can be processed and delivered to one of two locations in the MSL Analyti-cal Laboratory (AL): the MSL CheMin (XRD/XRF) experiment will provide definitive mineralogy, while the Sample Analysis at Mars (SAM) instrument suite will measure the chemical and isotopic composition of volatile species.

Evolved gas analysis by SAM: The Mars Science Laboratory utilizes a highly mobile rover and a sophis-ticated set of sample acquisition, screening, and proc-essing tools. Selected samples will be examined with advanced laboratory-like analytical instruments to as-sess sites on Mars as potential habitats for past or pre-sent life, through the most comprehensive geological and chemical analysis possible within the constraints of in situ robotic investigation. The SAM instrument suite includes an evolved gas analysis (EGA) meas-urement mode in which volatiles released from rocks and fines are continuously sampled by a quadrupole mass spectrometer or a tunable laser spectrometer as sample temperature is raised from ambient to 1100 °C.

Although the Viking landers heated sampled fines in several experiments on each lander and detected evolved CO2 and H2O [10], these experiments were primarily designed to search for organic molecules and did not continuously sample gases evolved in a con-trolled temperature ramp. As previously demonstrated [11] in laboratory experiments designed to support first the Mars Polar Lander and later the Phoenix TEGA and MSL/SAM experiments, the rich EGA spectra of sulfate compounds are quite informative, as they can reveal the degree of weathering based on the water structurally incorporated into these materials. As the temperature of the sample is increased, the water of hydration is released first, followed by eventual break-down of the sulfate to produce SO2. The degree of incorporation of water into the mineral structure is revealed in the temperature of its release for each sul-fate type.

Our EGA experiments are presently being imple-mented on a breadboard of the SAM suite to allow optimization of experimental parameters. Sulfate ana-logs include jarositic tephras from Hawaii with differ-ent degrees of aqueous alteration.

Preservation environments for organic mole-cules: One of the primary goals of SAM is to search for reduced carbon compounds and, if these are found, to understand their source and their transformation processes in the martian chemical environment. Tere-strial microbes often thrive in sulfate-rich environ-ments and an improved understanding of the long- term preservation potential of residue organics in Mars analog sulfate environments is critical in this regard [12, 13].

References: [1] Clark, B.C. et al. (1982) JGR, 87, 10059. [2] Trieman, A.H. et al. (1993) Meteoritics, 28, 86. [3] Farquhar, J., et al. (2000) Nature, 404, 50. [4] Foley, C.N. et al. (2003) JGR, 108, E12, 8096. [5] Klingelhofer, G. et al. (2004), Sci. 306, 1740. [6] Squyres, S.W (2004) Sci., 306, 1709. [7] Ming, D.W. (2006) JGR, 111, EO2S12. [8] Gendrin, A. et al. (2005) Sci., 307, 1587. [9] http://mars.jpl.nasa.gov/msl [10] Biemann, K. (1976) Sci., 194, 72. [11] Ming, D.W. et al., LPSC XXXIV, Abstract #1880 (2003). [12] Sumner, D. Y. (2004) GGR, 109, E12007. [13] Aubrey, A. et al. (2006) Geology, 34, 357.


SULFATE DEPOSITS AND GEOLOGY OF WEST CANDOR CHASMA, A CASE STUDY. N. Mangold1, A. Gendrin2, C. Quantin1,3 , B. Gondet2 and J.-P. Bibring2 and the OMEGA Co-Investigator Team (1) IDES-Orsay, UMR 8148, CNRS and Université Paris -Sud, Bat. 509, 91405 ORSAY Cedex, France, [email protected] -psud.fr (2) IAS, Université Paris-Sud, France, (3) CEPS, Smithsonian Institute, Washington DC.

OMEGA Analysis: Sulfates are identified on many areas of the Valles Marineris region, with broad outcrops in the Candor Chasma region [1]. The match between the spectra and the spectrum of kieserite is excellent between 1.4 and 2.5 µm, with three main absorption bands at 1.6, 2.1 and 2.4 µm. These bands are due, in monohydrated sulfates, to the single, strongly hydrogen bonded, water molecule. A second group of minerals is detected in West Candor with absorption bands at 1.4 and 1.9 µm and a drop at 2.4 µm. Such associations are observed in spectra of polyhydrated sulfate minerals. Additionally, a drop between 1 and 1.3 micron suggests the frequent occurrence of iron oxides close to the locations where sulfates are detected. Notice also that sulfates might not be the only minerals present, especially if the rocks contain minerals that are spectrally neutral in the NIR wavelengths (halite salt or silica for example). On the other hand, darker parts and canyon floor mainly correspond to eolian mantling do not show any sulfates but most often pyroxenes signatures. Comparison with geology: The most striking result of the identification of sulfates is their systematic correlation with interior layered deposits (ILD) which cover more than half of the West Candor Chasma surface (Fig. 1) [1,2]. At MOC scale, the surface texture of bright deposits displays flutes and yardangs typical of eolian erosion in weakly consolidated material. They are also devoid of small impact craters (< 100 m), which does not mean that the layers formed recently, but that they were exhumed recently. When compared to albedo and thermal inertia, sulfates are detected over terrains significantly bright (albedo :0.15-0.25) and with thermal inertia of 250-450 usi showing the lack of dust and a relative induration of the material. A detailed look to the eastern mesa shows a pile of layers reaching more than 3 km over which sulfates are present. We observe that deep band depths of kieserite are present on steep slopes (> 15°). In order to quantify this observation we compared the relative proportion of kieserite-rich areas relative to ILD mapped from images. This histogram shows a continuous increase in the relative proportion of kieserite with the increase of the slope. At 20 to 25° of slope, kieserite cover 60 to 80% of the ILD unit whereas only 20% at 5°. This effect is not observed for the polyhydrated sulfates showing this is not a statistical bias. The effect of steep slopes is mainly to provide more freshly eroded material at outcrops. The increasing presence of kieserite there is thus an evidence that kieserite is

directly present in the bedrock and does not come from surface interactions. Conclusion: The detailed study of West Candor Chasma shows that sulfates are in the bedrock of interior layered deposits with kieserite more frequent on freshly eroded bright scarps.

Fig. 1: Identification of kieserite (red) and polyhydrated sulfates (green) by OMEGA/MEX in West Candor Chasma. The brighter red corresponds to deeper depth of the main absorption band at 2.1 micron for kieserite.

Fig. 2: Proportion of each sulfates ratioed by the total proportion of ILD versus slope (1 means kieserite on all ILD outcrops mapped from geology). Kieserite becomes more and more frequent as the slope increases. Strong variations for slopes >30° are due to statistical unsampling of slopes of such steepness. References: [1] Gendrin et al, Science, 307, 1587-1591, 2005. [2] Quantin et al, this issue.


SULFATE GEOCHEMISTRY AND THE SEDIMENTARY ROCK RECORD OF MARS S. M. McLennan1,J. P. Grotzinger 2, J. A. Hurowitz1 and N. J. Tosca1; 1Department of Geosciences, SUNY at Stony Brook, StonyBrook, NY, 11794-2100, USA ( [email protected] ; [email protected] ;[email protected] ); 2Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena,CA, 91125, USA ( [email protected] ).

Carbonate Earth vs. Sulfate Mars?: Terrestrialsurficial processes are controlled by the carbon cycle.Early in Earth history, the bulk of Earth's carbon wassequestered into carbonate rocks and reduced carbon-bearing sediments. CO2 derived from volcanism andrecycling of carbon-bearing sedimentary rocks dis-solves in water to produce weak carbonic and organicacids that are the primary agents of rock weathering.Carbonate equibria buffers the pH of the marine sys-tem to about 8.2 and the overall effect is that the pH ofmost terrestrial aqueous systems is in the narrow mod-erate range of 5-9. Low pH settings are restrictedmostly to environments where sulfur cycling locallydominates (e.g., acid mine drainage, acid lakes, craterlakes). Another effect is that the chemical sedimentaryrock record is dominated by carbonates (limestones,dolostones) with sulfates, mostly evaporites, being anorder of magnitude less abundant.

Apart from minor occurrences in SNC meteorites,no carbonates have been unambiguously identified onMars. Instead, spectral and geochemical evidencepoints to a variety of Mg-, Ca- and Fe-sulfates ofevaporitic origin on the surface of Mars throughout itshistory. This fundamental contrast with the terrestrialsituation suggests that the sulfer cycle rather than thecarbon cycle dominates surficial processes on Marsand that sulfates may dominate the chemical sedimen-tary record. Even in the presence of a CO2-bearingatmosphere small amounts of SO2 would lead to verylow pH aqueous conditions. For example, pure waterin equilibrium withan atmosphere containing 10-5 atmSO2 (~10 ppm) has a pH of 2.9.

Acid Sulfate Alteration on a Basaltic Planet andthe Martian Sedimentary Rock Record:. Chemicalweathering of the terrestrial granodioritic upper crust atmodest pH results in abundant siliciclastic sedimentcomposed of quartz, residual clays and oxides and K-feldspar. Chemical constituents (carbonate, evaporite,chert) compose only 15-20% of the sedimentary re-cord. In contrast, the martian exposed crust is basalticin character with relatively labile olivine, Fe-Ti oxides,plagioclase and pyroxene being abundant and chemi-cally resistant quartz and K-feldspar being absent.Dissolution rates of most basaltic minerals are ordersof magnitude greater than quartz and K-feldspar. Ac-cordingly, for a given amount of water that interactswith martian crust, chemical weathering, under low pH

conditions, coupled with a primary basalt lithology,should be fundamentally more efficient than on Earth.

The fate of dissolved constitutents by deposition ofMg-, Fe- and Ca-sulfate evaporites appears well doc-umented. (One caveat is that freezing can also producebrines from which evaporite minerals could precipi-tate.) Another abundant product of chemical weather-ing of basalt is amorphous silica and there is growingevidence that such deposits exist. Accordingly, thechemical sedimentary record likely includes bothevaporites and secondary silica as major constituents.

The nature of the martian siliciclastic rock record isless clear. At low pH, Al and Fe are soluble and for-mation of residual aluminous clays and secondary ox-ides should be inhibited. There is growing evidencefor clay minerals on at least local scales but large scalechemical fractionation of Al during sedimentary proc-esses appears to be absent. Accordingly, the siliciclas-tic component of the martian sedimentary record maybe characterized by a dearth of secondary and resistateminerals and thus dominated by relatively unweatheredbasaltic material.

Amazonian Acid Sulfate Alteration and SulfateRecycling Processes: Wherever examined, rocks onthe present martian surface have thin mm-scale altera-tion rinds characterized by elevated S and Cl. Geo-chemical differences between brushed and abradedigneous rock surfaces are consistent with alterationdominated by very low fluid/rock ratio and low pHfollowed by evaporation, physical erosion and soil ad-hesion. The origin of fluids that give rise to this rela-tively young alteration is not known but most workersappeal to SO2 volcanic emissions, analogous to acidsulfate alteration observed on young Hawaiian volca-noes and elsewhere. There is geomorphological evi-dence for young volcanism on Mars and isotopic sys-tematics of shergottites are interpreted by most to indi-cate young crystallization ages, thus adding plausibilityto the occurrence of young volcanic gases in the mar-tian atmosphere. An alternative (or additional) sourcefor young widely dispersed acidic fluids is recycling ofancient sulfate deposits by impact processes. Sedi-mentary sulfates, especially Fe-sulfates, release con-siderable amounts of acidity when dissolved in water.Such a process would be limited by the availability ofwater, which could come from hydrated evaporiteminerals (M2+SO4•nH2O) or from subsurface water.


EXTRA-MARTIAN ORIGNS OF C, FE, NI, S and CL ELEMETS TO FORM DEPOSITS AS LOCAL CYCLE SYSTEM ON MARS. Yasunori Miura, Inst. Earth Sciences, Graduate School of Science & Engineering, Yamaguchi University, Yoshida 1677-1, Yamaguchi, 753-8512, Japan, [email protected]

Introduction: There are many Fe-rich minerals including sulfate mineral of jarosite [1] found on Martian surface by previous robotic explorations. Simple interpretation of sulfate minerals on Mars, compared with Earth, will discuss sources of these elements of Fe, Ni , S and Cl to Mars. The purpose to this paper is to elucidate extra-Martian sources of Fe, Ni, S and Cl elements to form sulfate minerals as comparison with various terrestrial minerals. Present special carbon cycle of Martian system: On present Mars without wide sea water, major two (large and mall) carbon cycle systems on Earth [2-7] cannot be expected to find except Polar Regions of Mars as special carbon cycle system (C-O) between air (carbon oxides) and Polar ices (solid carbon dioxides).

Carbon from cycle system on Mars: As there are few oxygen and nitrogen on Mars in large cycle system, there is no active living species of plants with photosynthesis to produce oxygen on Mars. This is mainly because carbon-bearing carbonate rocks of limestone blocks formed in wide sea water (as in active plate crust of Earth) cannot be found so far on Martian surface. Size of bio-minerals formation from cycle system is considered to be 1) local formation at deeper mantle rocks (mainly by local water or fluid carbon dioxides), or 2) wide formation of carbonate minerals with Fe-rich surface.

Extra-Martian sources of C on primordial Mars: From large carbon cycle system of Mars in the Solar System, C and H elements of Mars are considered to be supplied originally from 1) older rocks of Mars to evaporate to form gas (CO, CO2, H2O etc.) and fall as rain water to deposit as bio-minerals on Martian surface, and 2) impact explosions with Mars of C-H-O-rich gas collided with carbonaceous meteorites from asteroids and comets, together with breaking blocks before impacts. As there are few relict rocks of pure carbonate minerals (except spherules of ALH84001 meteorite [8]), extra-Martian sources of C element by carbonaceous meteorites and comets are explained to start active reaction among gas, liquid and solid states during shock wave impact event at local range (including local fluid formation).

Elements of Fe, Ni, S and Cl rich in meteorite compared with the terrestrial crust: Apollo lunar samples indicate extra-lunar elements of Pt-group elements and so on from meteorites are found in breccias samples [9]. From elemental abundances of carbonaceous meteorite and terrestrial crusts [10] which will be applied to Martian surface. Fe is 3 times higher (than terrestrial crust) , S is 82 times higher, Cl

is 1.5 times higher, C is 5.8 times higher, and Ni is 138 times higher than crust of Earth. In fact, sulfate minerals [11] found at impact crater sites by instruments on current rovers and orbiter spacecraft (NASA-JPL). Formation of sulfate minerals in fluid conditions on Mars: Sulfate minerals on Mars are considered to be formed from impact-induced elements of meteorites with fluid conditions before or after initial impact events. Fluid conditions on Mars are proposed by an impact condition including comets with C, H and O. Resources of elements and living species on

Mars: Impact process is cycle system on planet without active volcano [12]. Mars is not active planet, except relicts of old volcanism. Numerous impact events on Mars are considered to be formed concentration of elements (i.e. Fe oxides and sulfate minerals). Living species at primordial stage are formed as local reaction and area on Mars.

Summary: The present results are summarized as follows: 1) Extra-Martian sources of carbon by carbonaceous meteorites and comets are considered to be during shock wave impact event at local range. 2) Elements of Fe, S and Cl are rich in carbonaceous meteorite than terrestrial crusts, which is applied to Martian surface to form sulfate minerals. 3) Sulfate minerals on Mars are considered to be formed from impact-induced elements of meteorites with fluid conditions before or after initial impact events including comets.

References: [1] Kato.T and Miura Y. (1977) Mineralogical Journal (Japan), 8, 419-430. [2] Miura Y. (2006) Antarctic Meteorites (NIPR, Tokyo), 73-74. [3] Miura Y. (2006), LPS XXXVII, abstract （LPI/ USRS, USA). CD #2441.[4] Miura Y. (2006) 2nd Hayabusa Symposium (Univ. Tokyo), 49-50. [5] Miura Y. (2006): ICEM2006 symposium abstract paper volume (Yamaguchi University, Yamaguchi, Japan) 112-113. [6] Miura Y. (2006): Workshop on Spacecraft Reconnaissance of Asteroid and Comet Interiors ).CD#3008. [7] Miura Y. (2006): ICEM2006 symposium abstract paper volume (Yamaguchi University, Yamaguchi, Japan) 102-103. [8] McKay D.S. et al. (1996): Science, 273, 924-930. [9] Heiken G.H. et al. (1991): Lunar Sourcebook (Cambridge Univ. Press), 357-474. [10] Univ. Sheffield (2006): Periodic table web- elements. http://www.webelement.com. [11] Bishop J. L. et al. (1998) J.G.R., 103, 31457- 31476. [12] French B. M. (1998) Trace of Catastrophe. LPI Contribution No.954 (LPI, Houston, USA). pp. 120.


MARS-ANALOG BRINES AND EVAPORITE EXPERIMENTS: IMPLICATIONS FOR SULFATES. J. M. Moore1 and M. A. Bullock2, 1NASA Ames Research Center, M/S 245, Moffett Field, CA 94035; [email protected], 2Southwest Research Institute, 1050 Walnut St., Suite 400, Boulder CO 80302; [email protected].

Introduction: For the past 7 years we have been

producing Mars-analog brines and evaporites in the laboratory under strictly-controlled Mars simulated conditions. We generated Mars-analog brines by al-lowing a mixture of minerals derived from SNC min-eralogy [1] to soak in pure water under a synthetic current-Mars atmosphere [2] and under a gas similar to the present Mars atmosphere but with added acidic gases [3]. We then produced evaporitic assemblages by allowing these brines (or synthetic versions of them) to dry out under both kinds of atmosphere, ei-ther by direct evaporation or by freezing followed by sublimation.

Laboratory Mars Brines: In our first set of labo-ratory experiments we allowed an SNC-derived min-eral mix to react with pure water under a simulated Mars atmosphere of modern composition for 7 months. These experiments were performed at one bar and at three different temperatures in order to simulate the subsurface conditions that most likely exist where liq-uid water and rock interact on Mars today. The domi-nant cations dissolved in the solutions we produced, which may be characterized as dilute brines, are Ca2+, Mg2+, Al3+ and Na+, while the major anions are dis-solved C, F-, SO4

2- and Cl-. Typical solution pH was in the range of 4.2-6.0. Abundance patterns of ele-ments in our synthetic sulfate-chloride brines are dis-tinctly unlike those of terrestrial ocean water or conti-nental waters, however, they are quite similar to those measured in the martian fines at the Mars Pathfinder and Viking 1 and 2 Landing sites. This suggests that salts present in the martian soils may have formed over time as a result of the interaction of surface or subsur-face liquid water with basalts in the presence of a mar-tian atmosphere similar in composition to that of to-day. If most of the mobile surface layer was formed during the Noachian when erosion rates were much higher than at present, and if this layer is roughly ho-mogeneous in salt composition, the total amount of salt in the martian fines is approximately the same as in the Earth's oceans.

In a second set of laboratory experiments we al-lowed an SNC-derived mineral mix to react with pure water under a simulated Mars atmosphere containing the added gases SO2, HCl and NO2. The addition of acidic gases was designed to mimic the effects of vol-canic gases that may have been present in the martian atmosphere during periods of increased volcanic activ-

ity. The experiments were performed at one bar and at two different temperatures. The dominant cations dis-solved in the solutions we produced were Ca2+, Mg2+, Al3+ and Na+, while the major anions are dissolved C, F-, SO4

2- and Cl-. Typical solution pH was in the range of 3.6-5.0. Abundance patterns of elements in these enhanced sulfate-chloride brines were also unlike those of terrestrial ocean water, terrestrial continental waters, but also unlike those measured in the martian fines at the Mars Pathfinder and Viking 1 and 2 Land-ing sites. In particular, the S/Cl ratio in our experi-ments was about 200, compared with an average value of approximately 5 in martian fines.

The results of these two sets of laboratory Mars-brines experiments provide evidence that salts seen on much of the planet were created under atmospheric conditions similar to today. This suggests that salts present in the martian soils, such as those seen by MER Spirit may have formed over time as a result of the interaction of surface or subsurface liquid water with basalts in the presence of a martian atmosphere similar in composition to that of today, rather than with an atmosphere higher in acidic volatiles. This environment is distinctly different than the acid-rich environment which we hypothesize [4, 5] existed when the massive layered evaporates observed by MER Op-portunity and the Mars Express Omega spectrometer were formed.

Laboratory Mars Evaporites: Our initial evapo-rates experiments involved the rapid evaporation of synthetic brines formed under simulated present-day atmosphere of Mars [2]. The precipitate was analyzed using X-Ray Diffraction. The predominant phase is gypsum, which occurs with a mixture of hydrous sul-fates such as hexahydrite (MgSO4.6H2O), and possibly mirabilite (Na2SO4.10H2O), and starkeyite (MgSO4.4H2O). Calcite is probably present in very small amounts and magnesian calcite, sylvite and hal-ite were found in very small amounts. Ongoing ex-periments are investigating the relative stability of sul-fate and carbonates under simulated Mars conditions.

References: [1] McSween H.Y. (1985) Reviews of

Geophysics, 23, 391-416. [2] Bullock M.A. et al. (2004) Icarus, 170, 404-423. [3] Bullock M.A. and Moore J.M. (2004) GRL, 31, L14701. [4] Moore, J.M. (2004) Nature, 428, 711-712, [5] Bullock M.A. and Moore J.M. (2006) abstract, this conference


IRON SULFATES AT GUSEV CRATER AND MERIDIANI PLANUM, MARS. Richard V. Morris1 and Athena Science Team, 1ARES NASA Johnson Space Center, Houston, TX 77058 ([email protected]).

Introduction: The abundance and speciation (oxi-

dation and coordination state and mineralogical compo-sition) of both Fe and S are parameters that characterize the formation conditions of primary rock lithologies and the style, extent, and timing of weathering and altera-tion. The parameters directly address a major scientific objective of the Mars Exploration Rover (MER) mis-sion, which was to characterize the atmosphere and sur-face of Mars, searching for evidence of aqueous activity [1,2]. The MER rovers Spirit (Gusev crater (GC)) and Opportunity (Meridiani Planum (MP)) carried Alpha Particle X-Ray (APXS) and Mössbauer (MB) spec-trometers for elemental analysis and Fe speciation, re-spectively [1,2]. Summarized here is evidence largely from [3-7] for the presence of Fe-bearing sulfates at the GC and MP landing sites through sols 723 and 560, respectively.

Discussion: Total Fe concentration and Fe-oxidation state are shown as a function of SO3 concen-tration in Fig. 1. The Burns formation outcrop at MP and the PasoRobles class soils at GC have exceptionally high SO3 concentrations (up to ~28 and 34 % SO3, re-spectively). The high Fe-oxidation state (Fe3+/FeT ~0.7-0.9) implies that sulfur is present as the sulfate anion ((SO4)-2). Their MB spectra (Fig. 2a and 2b) and charac-terizing MB parameters (isomer shift δ and quadrupole splitting ∆EQ) are also distinctive. The MB parameters for MP (δ ~0.38 mm/s and ∆EQ ~1.22 mm/s) are consis-tent with the presence of jarosite ((K,Na,H3O)(Fe,Al)3(SO4)2(OH)6) with Fe>>Al, and those for GC (δ ~0.42 mm/s and ∆EQ ~0.60 mm/s) are consistent with octahedrally-coordinated Fe3+ in a sul-fate. The mineralogical composition of the GC Fe3+-sulfate is not constrained, but available MB evidence [8,9] is not consistent with the simple anhydrous sulfate Fe2(SO4)3. Jarosite (and probably the GC Fe3+-sulfate) are evidence for aqueous alteration, probably under acid-sulfate conditions.

Basaltic soils at GC and MP (Laguna class soil) have ~2 – 15% SO3. The concentration of Fe associated with the nanophase ferric oxide doublet (δ ~0.38 mm/s and ∆EQ ~0.6 - 1.0 mm/s; Fig. 2c) increases with the SO3 concentration (see [5,7]), suggesting that npOx is also a sulfate-bearing phase. The unidentified ferric doublet Fe3D3 at MP may also be sulfate-bearing.

References: [1] Squyres S. W. et al. (2004) Science, 305, 794. [2] Squyres S. W. et al. (2004) Science, 306, 1698. [3] Morris R. V. et al. (2004) Science, 305, 833-836. [4] Klingelhöfer G. et al. (2004) Science, 306, 1740-1745. [5] Morris R. V. et al. (2006) JGR, 111, E02S13,

doi:10.1029/2005JE002584. [6] Morris et al. R. V. (2006) JGR, submitted. [7] Yen A. S. (2005) Nature, 436|7, doi:10.1038/nature03637. [8] Long G. J. et al. (1979) Inorg. Chem., 18, 624. [9] Morris R. V., unpublished results.

0

10

20

30

40

0 5 10 15 20 25 30 35

Fe2O

3 +

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t%)

MP Soil GC SoilMP Rock GC Rock

(Fig. 1a)

Jarosite(MP Outcrop) Fe(3+) Sulfate

(GC PasoRobles Soil)

SO3 (wt%)

0.0

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+)/F

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Fe(3+) Sulfate(GC PasoRobles Soil)

OlPxnpOxFe3+ SulfateJarFe3D3HmMt0.02

B032RR0McKittrick_MiddleRAT

200-270 K

(Fig. 2a)

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C -

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B060SU0 MountBlanc_LesHauches 200-280 K

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0.02

(Fig. 2b)


LOOKING FORWARD TO CRISM. S. Murchie1, R. Arvidson2, P. Bedini1, J.-P. Bibring3, J. Bishop4, P. Caven-der1, T. Choo1, R.T. Clancy5, D. Des Marais4, R. Espiritu6, R. Green7, E. Guinness2, J. Hayes1, C. Hash6, K. Heffer-nan1, D. Humm1, J. Hutcheson1, N. Izenberg1, E. Malaret6, T. Martin7, J.A. McGovern1, P. McGuire2, R. Morris8, J. Mustard9, S. Pelkey9, M. Robinson10, T. Roush4, F. Seelos1, S. Slavney2, M. Smith11, W.-J. Shyong1, K. Strohbehn1, H. Taylor1, M. Wirzburger1, and M. Wolff5, 1Applied Physics Laboratory, Laurel, MD, 20723, [email protected]; 2Washington University, St. Louis, MO; 3Institut d'Astrophysique Spatiale, Orsay, France; 4NASA/ARC, Moffett Field, CA; 5Space Science Institute, Boulder, CO; 6Applied Coherent Technology, Herndon, VA; 8NASA/JSC, Houston, TX; 9Brown University, Providence, RI; 10Northwestern University, Evanston, IL; 11NASA/GSFC, Greenbelt, MD; 7NASA/JPL, Pasadena, CA.

Instrument: The Compact Reconnaissance Imag-

ing Spectrometer for Mars (CRISM) [1] is a hyper-spectral imager on the MRO spacecraft. CRISM con-sists of three subassemblies, a gimbaled Optical Sensor Unit (OSU), a Data Processing Unit (DPU), and the Gimbal Motor Electronics (GME). Spectral coverage is 362-3920 nm with sampling at 6.55 nm/channel. Spa-tial sampling is 15-19 m/pixel .

Measurements: CRISM's objectives are (1) to map the entire surface using a subset of bands to char-acterize crustal mineralogy, (2) to map the mineralogy of key areas at high spectral and spatial resolution, and (3) to measure spatial and seasonal variations in the atmosphere. These objectives are addressed using three major types of observations. In multispectral survey mode, with the OSU pointed at planet nadir, data are collected at a subset of 73 channels covering key min-eralogic absorptions, and binned to pixel footprints of 100 or 200 m/pixel. Nearly the entire planet can be mapped in this fashion. In targeted mode, the OSU is scanned to remove most along-track motion, and a region of interest is mapped at full spatial and spectral resolution (545 channels). Ten additional abbreviated, spatially-binned images are taken before and after the main image, providing an emission phase function

(EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects (Figure 1). In atmospheric mode, only the EPF is acquired. Global grids of the resulting lower data volume observations are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties.

Hydrated Minerals: Detection of sulfates and phyllosilicates by OMEGA [2] drove both the selection of wavelengths in the multispectral survey and the se-lection of preliminary sites for targeted observations. Pelkey et al. [3] used OMEGA data to refine the initial selection of multispectral wavelengths to adequately sample these minerals' diagnostic absorptions (Figure 2), and formulated a set of standard parameters to rep-resent occurrences of these minerals in map form. From those maps, thousands of targets have been iden-tified for targeted observation at CRISM's full spatial resolution. In the 99% of the planet not targeted, occur-rence of sulfates and phyllosilicates will be mapped at 2-20 times the resolution of OMEGA. These data will provide improved understanding of distributions and spatial relations of Martian aqueous minerals.

References: [1] Murchie S. et al. (2006) JGR, in press. [2] Bibring J.-P. et al. (2005) Science, 307, 1576-1581. [3] Pelkey S. et al. (2006) JGR, in press.

Figure 1. During overflight of a target, five short incoming (red) and outgoing (blue) scans across the target are performed during which data are taken spatially binned. At the time of target closest ap-proach, a slow scan is performed at full spatial resolution (green).

Figure 2. Reflectance spectra of sulfate and phyllosilicate minerals over CRISM's spectral range.


MULTI-INSTRUMENT SULFATE DETECTION AND MINERAL STABILITY ON MARS. J. F. Mustard 2, 1ADepartment of Geological Science, Brown University, Providence, RI 02912 ([email protected])

Introduction: While sulfate minerals have been

long been predicted to be present in martian surface materials, it has only been in the last five years that sulfate minerals have been unambiguously detected. Importantly, these detections have been achieved using a variety of instruments including orbital data spanning the electromagnetic spectrum (thermal IR, [1]; visible-near infrared (VNIR), [2] [3]) and instruments on landed science packages (Mössbauer, [4]; APXS [5], Mini-TES [6]). These results provide multiple lines of evidence for the presence of sulfate, as well as defining which sulfate minerals are stable on the surface of Mars. In this abstract I consider the range of sulfate minerals detected from remotely sensed and other in-struments in the context of remotely sensed detectabil-ity, uniqueness, and stability.

Sulfate Detected: The OMEGA instrumet on the Mars Express spacecraft has detected sulfate mineals on the basis of absorption bands in the VNIR wave-length region [2]. These data uniquely identify the Mg-sulfate kieserite [3] which contains 1-H2O and the Ca-sulfate gypsum [7] which contains 2-H2O. Another class of sulfate is identified that is referred to as poly-hydrated sulfate for which neither the degree of hydra-tion nor coordinating cation can be uniquely resolved with existing data [3]. Thermal infrared data from TES provide evidence for sulfate in mineral deconvoutions. For these orbital observations the model abundances are at the detection limit of the instrument and method [1]. Mini-TES data show clear signatures of sulfate based on a distinct shoulder in the spectra near 8 µm and show model abundances up to 35% [6]. Thermal IR analyses are not as specific as to the type of sulfate present though Mg and Ca sulfate minerals are typi-cally identified.

Interestingly, Mössbauer spectroscopy has identi-fied jarosite on the basis of the iron mineralogy in the sediments in Meridiani [4]. Mössbauer spectroscopy is not sensitive to Fe-free sulfate minerals such as kie-serite and gypsum and the amount of jarosite present is not precisely known. However, the amount of sulfer detected with the APXS instrument requires abundant sulfate to accommodate the detected sulfer levels [5] and Mg- and Ca-sulfates are expected on the basis of the APXS measurements.

Detectability: The ability to detect the presence of sulfate varies among these instruments. Instrumental and observational effects (e.g. signal to noise, atmos-pheric dust or ice clouds) will affect observations. For the VNIR, only water- or hydroxyl-bearing sulfates

exhibit absorptions and thus sulfate minerals such an-hydrite would not be detected. Thermal IR is sensitive to hydrous and anhydrous sulfates, but absorption fea-tures are strongly affected to surface texture and parti-cle size. Mössbauer is only sensitve to Fe-bearing sul-fate minerals. Nevertheless, the remote sensed instru-ments do present a consistent set of results indicating the presence of sulfates in the Meridian region from the outcrop to orbital scale.

Stability: Many water-bearing sulfates are in dy-namic equilibrium with their environment, particularly affected by the relative humidity. On the martian sur-face, relative humidity can cycle between 1% and 100% on time scales as short as a day as well as on orbital time scales [8]. [9] showed that hydrated sul-fates will readily dehydrated under martian low hu-midty conditions, often becoming amorphous. Upon rehydration under high humidty conditions, the amor-phous state is maintained.

Discussion and Conclusions: The detection of sulfate minerals by orbital and landed science instru-ments are in general agreement. Gypsum and kieserite are clearly identified from orbit and jarosite from the Opprotunity rover. The VNIR spectrum of polyhy-drated sulfate is consistent with a range of sulfate chemistry and hydration states including the amor-phous forms of hydrated sulfate that might result from the cycling of humidty on the martian surface. The clear presence of kieserite and gypsum indicate that some well crystalline phases are stable on the surface. However, the polyhydrated sulfate minerals may be indicative of regions where amorphous hydrous sul-fates are present perhaps formed through humidty variations on geologic time scales. It is interesting to note that kieserite deposits are typically observed on fresh appearing outcrops, perhaps recently exposed by erosion while polyhydrated sulfates are on apparently more mature surfaces [10]. References: [1] Bandfield J. L. (2002) JGR 107, 5042, doi:10.1029/2001JE001510. [2] Bibring J.-P. et al. (2005) Science 307, 1576-1581. [3] Gendrin A. et al. (2005) Science 307, 1587-1591. [4] Klingelhöffer G. et al. (2004) Science 306, 1740-1745. [5] Rieder R. et al. (2004) Science 306, 1746-1749. [6] Christensen P. R. et al. (2004) Science 306, 1733-1739. [7] Langevin Y. et al. (2005) Science 307, 1584-1586. [8] Mellon M. T. and B. M. Jakosky (1995) JGR 100, 11781-11799. [9] Vaniman D. T. et al. (2005) LPSC 36, 1489. [10] Mangold N. et al. (2006) this volume.


F

THE CHALLENGE OF RETURNING HYDRATED SULFATES FROM THE SURFACE OF MARS TOEARTH. C. R. Neal1, 1Dept. of Civil Eng. & Geological Sciences, University of Notre Dame, Notre Dame, IN46556, USA, [email protected].

Introduction: The identification of Jarosite by theMER rovers produced intense excitement regarding theevolution of the Martian surafce and the fluid-rockinteractions that occurred to produce the sequence onMeridiani Planum [1]. This mineral and those associ-ated with the Alunite Supergroup can contain impor-tant trace elements useful for isotopes studies (e.g.,Sm-Nd) as well as useful chronomters (e.g., K-Ar andAr-Ar). While advances have been made is roboticsurface instrumentation, it is inevitable that in order todiscern the potential information contained in thesesulfates, analyses using terrestrial laboratories will berequired in order to produce high precision and accu-racy for the results. This requires sample return andraises the question: How will we know that Martiansamples returned to Earth are still in their pristine (i.e.,Martian surface) condition? This presentation is a con-tinuation of the CAPTEM-initiated paper regardingMars Sample Return [2]. It focuses on the issues ofsampling caching, and return of sulfate samples.

Minerals of the Jarosite-Alunite Subgroups:The alunite supergroup contains over 40 minerals withthe general formula DG3(TO4)2(OH,H2O)6, where D =mono- (K, Na, NH4, Ag, Tl, H3O), di- (Ca, Sr, Ba, Pb),tri- (Bi, REE); G = usually Al or Fe3+; T = S6+, As5+, orP5+, with subordinate amounts of Cr6+, or Si4+ [3]. The

Al:Fe3+ ratio determines whether minerals are in thejarosite or alunite families ([4 Dut]; Fig. 1). Jarositehas trigonal symmetry [5] and its structure allows thesubstitution of many elements [6].

Challenges: Several papers written since the dis-covery of Jarosite (and potentially other hydrated sul-fates) on Mars have noted that this mineral can be usedto obtain age data using argon methods (e.g., [6]). Dataindicate little to no Ar loss at 90˚C for 12-14 hours [7].Dehydration of Jarosite from the hydronium site occursat 260˚C and dehydroxylation occurs between 450-480˚C [8]. For other hydrated sulfates, the situation isradically different. Hexahydrite (MgSO4.6H2O) formsfrom Epsomite (MgSO4.7H2O) at 16-20˚C at relativehumidities <60%. Kieserite (MgSO4.H2O) forms fromHexahydrite as relative humidity drops below 20-45%[9,10]. Hexahydrite dehydrates rapidly (≤24 hours) to avariety of secondary products (Starkeyite: 4 H2O;Sanderite: 2 H2O; Kieserite: 1 H2O) at 75˚C [11]. Suchchanges would radically affect H and O isotope com-positions especially if the sample cache was not sealed.

These examples demonstrate the need to under-stand mineral stability in order to maintain their pris-tinity once they have left the Martian surface. WhileJarosite appears to be quite robust, it is likely that thesamples will be in transit for at least 6 months, so weneed to know the kinetics of the dehydra-tion/dehydroxylation reactions and the closing tem-peratue for Ar in the mineral structure.

Sample Return Environment: Maintaining sam-ples returned from the Martian surface in their pristinestate is essential. By understanding the types of materi-als that are present on Mars is vital for engineering thesample return capsule. For the examples given above,the ideal situation would be to not allow the capsule toexceed the maximum surface temperature known onMars. Also, once the sample canister has been filled, itneeds to be sealed thus including Martian atmosphre atthe time of caching so the environment can be keptbuffered. Finally, monitoring the environment with thesample cache will be needed from the time it leavesMars until the time the arrive on Earth.

References: [1] Klingelhofer G. et al. (2004) Sci-ence 306, 1740-1745. [2] Neal C.R. (2000) JGR 105,22487-22506. [3] Stoffregen R.E. (1993) GCA 57 ,2417-2429. [4] Dutirzac J.B. & Jambor J.L. (2000)Rev. Min. Geochem. 40, 405-452. [5] Stoffregen R.E.et al. (2002) Rev. Min. Geochem. 40, 453-479. [6] Pa-pike J.J. et al. (2006) GCA 70, 1309-1321. [7] Vas-concelos P.M. et al. (1994) GCA 58 , 401-420. [8] Alp-ers C.N. et al. (1992) Chem. Geol. 96, 203-226. [9]Vaniman D.T. et al. (2004) Nature 431, 663-665. [10]Chipera S.J. et al. (2005) LPSC XXXVI, #1497. [11]Chipera S.J. et al. (2005) LPSC XXXVII, #1457.


CORRELATIONS BETWEEN SULFATE AND HEMATITE DEPOSITS AS OBSERVED BY OMEGA AND TES. E. Z. Noe Dobrea1, 1Malin Space Science Systems ([email protected]).

Introduction: Although crystalline grey hematite

has been detected in many of locations of the Valles Marineris system and adjacent chaotic terrain [1,2], its nature remains unknown to this day. Recent detections of sulfate-bearing minerals by the OMEGA spectrome-ter [3] have been found in some cases to correlate spa-tially with the TES hematite detections [4]. In such cases, they are associated with and with either layered outcrops or dark mantles at MOC resolution[4,5]. Here, we investigate the spatial extent of the correla-tion between TES hematite detections and OMEGA sulfate detections.

Methods and tools: We have used TES to gen-erate hematite index maps of the regions where [1] and [2] have reported the detection of crystalline grey hematite using TES. We then studied the same areas using available OMEGA data and compared our map-ping result to the TES hematite index maps.

Results: Our analysis suggests a strong corre-lation between TES hematite concentration and OMEGA sulfate mineralogy. All the high-resolution OMEGA observations of hematite-bearing regions have been found to also contain an enhanced sulfate signature, characterized by ~1.95-μm and a 2.4-μm bands (Fig. 1). The regions that do not show a signa-ture correspond to lower resolution OMEGA observa-tions, making comparisons difficult.

These deposits are associated to two types of ter-rains as observed by MGS/MOC: 1) a dark-toned man-tling material that is usually found in proximity to light-toned outcrops, and 2) an intermediate-toned outcrop that forms either stair-stepped or finely layered outcrops at MOC resolutions. It is not clear whether the outcrops are intrinsically intermediate in tone or whether they are lighter-toned outcrops that are sprin-kled with a venner of darker material, but their prox-imity to dark mantling material in MOC images sug-gest the latter.

Mineralogy: The NIR spectra of the hematite-bearing regions is very similar from region to region (Fig. 1). Comparisons to spectral libraries shows that their signature is at least in part consistent with that of gypsum (CaSO4·H2O).

Stratigraphy: MOC data of these regions indi-cates that the hematite-bearing outcrops are not the only outcrops in the region. Instead, they are usually found in association to other outcrops, some of which display the near-infrared signature of other sulfates. The specific stratigraphic relationships between these outcrop units are complicated and are being studied.

Preliminary topographic analysis of their locations indicates that they are found at different elevations, suggesting that they formed indepdently from each other.

Figure 1. Continuum-removed spectra of hematite bearing regions in Valles Marineris and nearby chaotic terrains (top 5), and spectral library mineral reflectance for comparison (bottom 3). All spectra have been shifted for clarity.

Discussion: On Earth, gypsum is a very common

mineral, typically formed as an evaporite deposit in assocaition with sedimentary rock. It can be deposited in lake and sea water, in veins, from volcanic out-gassing, and in hot springs. The morphology and thickness of the gypsum- and hematite-bearing out-crops is consistent with the repeated deposition of sev-eral layers material, making it likely that it is part of a sedimentary deposit. We therefore speculate a forma-tive regime similar to that hypothesized for the out-crops at the Opportunity landing site.

References: [1] Christensen, P.R. et al. (2001), J. Goephys. Res 106; [2] Glotch, T.D. et al. (2005), AGU Fall, abstract # P21C-0160; [3] Gendrin, A. et al. (2005) Science 307; [4] Noe Dobrea, E.Z. et al (2006) LPS XXXVII, Abstract #2068; [5] Knudson and Christensen (2005) AGU Fall, abstract #P21C-0162.


TERRESTRIAL ANALOGS OF MARTIAN SULFATES: MAJOR AND MINOR ELEMENT SYSTEMATICS OF SELECTED JAROSITE SAMPLES. J.J. Papike1, P.V. Burger1, J.M. Karner1, C.K. Shearer1, and V.W. Lueth2. 1Astromaterials Institute, Dept. of Earth and Planetary Sciences, Univ. of New Mexico, Albuquerque, NM, 87131. 2New Mexico Bureau of Geology and Mineral Resources, New Mexico Tech., Socorro, NM, 87801. Jarosite has been found to be an important phase at the Meridiani locality on Mars [1]. Papike et al. [2, 3] reviewed the potential of martian jarosite as a recorder of rock-fluid interactions by using terrestrial examples. Here we continue that research by discussing electron microprobe (EMP) analyses for 14 selected sample localities (Table 1). Another important use for jarosite is as a “Canary in a Mine” to detect potential toxins on the martian surface. An element of interest is arsenic and jarosite is a good recorder of the arsenic in the fluids from which it formed. We used a relatively broad beam for these analyses, between 10 and 30 microns (depending on grain sizes and texture), to avoid volatile loss of S, Na, and K. Thus the analyses average over most zoning features. EMP analyses show that these jarosites are mainly solid solutions between jarosite, KFe (SO+3

3 4)2(OH)6, and natrojarosite,

NaFe (SO+33 4)2(OH)6. Minor elements include Pb

in the 12-coordinated A-site, Al in the octahedral B-site, and P, As, Mo, and V in the tetrahedral T-site. Figures 1 and 2 show the variations of Na/(Na+K) atomic, and the range of P, As, Mo, and V in the T-sites, respectively. The tetrahedral site is an important player in these samples. Very high abundances of arsenic are detected in some samples, especially sample 1. In a companion abstract, Burger et al. [4] discuss oscillatory zoning of Na and K in a subset of these samples. This zoning was also documented by [3]. However, it should be noted [5] that 32 natural hydrothermal and supergene K- and Na- jarosites analyzed with XRD show <5% solid solution between the end-members. This indicates a very wide solvus (miscibility gap) and kinetics that allow phase separation on a submicron scale, even in samples that are still optically zoned and show chemical zoning by EMP with a 1 micron beam (EDS). REFERENCES [1] Klingelhofer et al. (2004) Science, 306, 1740. [2] Papike et al. (2006) GCA, 70, 1309. [3] Papike et al. (2006) AmMin, 91, 1197. [4] Burger et al. (this volume). [5] Desborough et al. (2006) ICARD, 458.

Table 1. Jarosite sample information. NO. SAMPLE LOCALITY1 8977 Mina la Mojina, Chih., Mexico2 PP01NV Post Pit, 5320 bench, NV3 AA01AZ AZ Apex Mine, AZ4 GH01UT Gold Hill -middle pit, UT5 AL01SP Almeiria, Spain6 H1 Gumma Fe Mine, Japan7 L1 Gumma Fe Mine, Japan8 MO01AZ Morenci Mine, AZ 9 98417129 Copiapo Mine, NM10 9841416 Sunshine #1, Bingham, NM11 SM01NM Sandia Crest, NM12 BC97-011 Bluestar Mine, NM13 GF-1 Goldfield, NV14 PB-1 Pena Blanca, Mexico

Jarosite 12-coordinated A-site occupancy

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1 2 3 4 5 6 7 8 9 10 11 12 13 14Sample number

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)

Figure 1.

1 2 3 4 8765 11109 12 13 141 2 3 4 8765 11109 12 13 14

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Jarosite tetrahedral site occupancy - P, V, As, Mo

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Figure 2.


JAROSITE-ALUNITE CRYSTAL CHEMISTRY. J.J. Papike ([email protected]), J.M. Karner, and C.K. Shearer, Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico 87131-1126. CRYSTAL CHEMISTRY. Although there are more than 40 mineral species with basically the alunite crystal structure [1], we emphasize alunite, KAl3(SO4)2(OH)6, natroalunite, NaAl3(SO4)2(OH)6, jarosite, KFe (SO+3

3 4)2(OH)6,

and natrojarosite, NaFe (SO+33 4)2(OH)6. We use

the general formula AB3(XO4)2(OH)6 [2] where A is a 12-fold coordinated site that can contain monovalent cations K, Na, Rb etc., divalent cations Ca, Pb, Ba, Sr, etc., and trivalent cations, REE, etc. The B position represents an octahedral site that usually contains trivalent Fe and Al but can include Zn2+, Mg2+, etc. The X position represents the tetrahedral site and contains S, P, As, Sb, etc. Our discussion of the crystal structure is derived from the discussions of Menchetti and Sabelli (1976) [3]. The structure drawing (Figure 1) projected down c, was kindly provided by Dr. Eric Dowty. The alunite-jarosite crystal structure is represented by space group R3 m, with Z = 3. For alunite there are 3 K, 9 Al, 18 (OH) groups, 24 O, and 6 S atoms per unit cell. The unit cell parameters [3] are alunite, a = 7.020 Å, c = 17.223 Å; Na-alunite, a = 7.010 Å, c = 16.748 Å; jarosite, a = 7.315 Å, c = 17.224 Å; Na-jarosite, a =7.327 Å, C = 16.634 Å. The

a-axis increases with the substitution of Fe3+ for Al in the octahedral site, and the c-axis decreases with the substitution of Na for K in the 12-coordinated site. Thus, these unit cell variations can be used for estimating the Na/K and Al/Fe3+ ratios in solid solution among the end-members alunite-natroalunite-jarosite-natrojarosite. The jarosite-alunite crystal structure is beautiful in its simplicity and truly remarkable (Figure 1) in that it can accommodate many elements in the periodic table. Figure 1 shows the jarosite structure projected down the c-axis. The K atom sits in a 12-coordinated site and is coordinated by 6 oxygen ligands and 6 OH ligands. All 6 oxygen ligands and all 6 OH groups are symmetrically identical. Thus the A-site has a highly symmetrical coordination with 6 identical K-OH bonds and 6 identical K-O bonds. For a more complete discussion of jarosite-alunite crystal chemistry see Papike et al. [4]. REFERENCES. [1] Alpers et al (2000) RIMS 40, 1-608. [2] Scott (1987) AmMin., 72, 178-187. [3] Menchetti and Sabelli (1976) N. Jahrb. Min. Monatsh. H. 9, 406-417. [4] Papike et al. (2006) GCA, 70, 1309-1321.

Figure 1.

a2

a1

a2

a1

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a1



Crystal Molds On Mars: Melting of a possible new mineral species to create martian chaotic terrain Ronald C. Peterson Department of Geological Science and Geological Engineering, Queen’s University, Kingston, Ontario, Canada, K7L 3N6 ([email protected]) Images sent back by the Mars Exploration Rover Opportunity from the Meridiani Planum show sulfate-rich rocks containing plate-shaped voids with tapered edges that are interpreted as crystal molds formed after a late-stage evaporite mineral has been re-moved (Herkenoff et al., 2004, 2006). Ex-perimental studies of the MgSO4 - H2O sys-tem at low temperatures reveal that the tri-clinic phase MgSO4·11H2O exhibits a crys-tal morphology that matches the shapes of these molds. MgSO4·11H2O melts incongru-ently above 2 °C to a mixture of 70% ep-somite (MgSO4·7H2O) and 30% H2O by volume. The latent heat of fusion is much lower than ice

Phase diagram for the MgSO4 - H2O system (after Hogen boom etal. 1995) The field of MgSO4·12H2O in the original reference has been relabeled as MgSO4·11H2O based on this work. MgSO4·11H2O melts incongruently to epsomite and a saturated solution at 2 °C (275 K) in this binary sys-tem.

When this occurs while crystals are encased in sediment, plate-shaped voids would remain. The existence of ice, low sur-face temperatures and the high sulfate content of surface rocks and soil on Mars makes MgSO4·11H2O a possible mineral species

near the surface at high latitudes or elsewhere in the sub-surface. If an evaporite layer con-tained a significant amount of this phase, in-congruent melting would result in a rapid re-lease of a large volume of water and could explain some of the landform features on Mars that are interpreted as outflow channels.

MgSO4·11H2O would not survive a sample return mission unless extraordinary precautions were taken.

Phase diagram illustrating the hydration/dehydration re-

lationships of MgSO4 as a function of temperature and rela-tive humidity (Chou and Seal 2003) The gray line indicates the conditions at the Viking Lander 1 site in summer (Savijarvi, 1995). A possible boundary for the epsomite - MgSO4·11H2O as a function of relative humidity is given as a dashed line by assuming it to be parallel to the kieserite – epsomite dehydration boundary. Dehydration / hydration rates are slow at these temperatures. Reactions would not reverse on a daily basis but in general temperature and rela-tive humidity conditions, at or below the surface at the Vi-king site, are such that either epsomite or MgSO4·11H2O will be the stable phase.

References Chou and Seal, 2003, Astrobiology, 3, 619. Herkenoff et al. 2004, Science, 306, 1727. Herkenoff et al.2006, LPSC XXXVIII, 1z816 Savijarvi 1995, Icarus 117,120.



GEOLOGY OF SULFATE DEPOSITS IN VALLES MARINERIS C. Quantin1,3, A. Gendrin

2, N. Mangold

3 , J-

P. Bibring2, E. Hauber4 and the OMEGA Team, 1 Center of Earth and Planetary studies, National Air & Space

Museum, Smithsonian Institution, Washington, D.C. 20013-7012, USA, 2IAS, Orsay, France,

3IDES, Orsay,

France, 4 DLR, Berlin, Germany,. [email protected]

Introduction: Valles Marineris exposes thick central

layered deposits named ‘’Interior Layered Deposits’’

(ILD). The origin and nature of the ILD of Valles

Marineris is one of the key issues of the canyon’s

evolution. First, from a geological point of view, there

is no consensus in their interpretation. The ILDs have

been interpreted as lacustrine deposits [i.e. 1,2], as

volcanic deposits [i.e. 3,4], or as aeolian deposits

[i.e.5]. Secondly, also in terms of their age, there is no

consensus. They are interpreted to be the Noachian

basement of Valles Marineris by some authors [6] or to

be subsequent to the opening of Valles Marineris and

thus Hesperian [i.e. 7].

OMEGA, the spectrometer onboard Mars Express, has

revealed sulfate signatures in association to these layer

deposits in Valles Marineris [8,9]. OMEGA detects

absorption bands typical of the monohydrated sulfate

Kieserite at 1.6, 2.1 and 2.4 µm and of polyhydrated

sulfates, with absorption bands at 1.4 and 1.9 µm and a

drop at 2.4 µm [8].

We focused on the geological context of the sulfate

signatures within Valles Marineris with respect to their

morphology, stratigraphy and also to their elevation

distribution. The objective is to understand the origin

of the sulfates in this part of Mars, as well as their

relationship with the ILD and the origin of the ILD.

Data set and method: Our present work is based on

multiple remote sensing data from the MGS, Mars

Odyssey and Mars Express missions. The different

data sets have been imported and integrated into a

Geographic Information System (GIS). Our GIS

superimposes for the entire Valles Marineris area: (1)

MOLA DEM, (2) the TES thermal inertia map, (3) a

mosaic of day-time THEMIS infrared, (4) a mosaic of

night-time THEMIS infrared images, (5) a mosaic of

HRSC images covering Valles Marineris, (6) the

available THEMIS visible images (7) all available

MOC images and (8) the mineralogy from OMEGA.

The mapping of sulfate spectral signatures has been

performed by [9] from OMEGA data. Although the

different observations are of different quality

(atmospheric conditions, observation time…) as

detailed in [9], the current updated OMEGA

mineralogical map gives us a good idea of the sulfate

distribution throughout the canyon system.

Results: Sulfates have been detected in all the canyons

of Valles Marineris, where sulfate signatures are

correlated to layered deposits [8,9]. The sulfates are

mainly located on the flanks of massive deposits and

on several isolated ILDs. Most of the OMEGA sulfate

signatures correspond to high thermal inertia areas

(>250 usi), and this is confirmed by morphology: the

sulfates detected by OMEGA correspond to outcrops

which are typically cliffs, with almost no impact

craters suggesting that they are extremely freshly

exposed.

The observation of MOC or HRSC images

corresponding to kieserite detections shows that the

kieserite mineral is correlated to massive light toned

material with yardang erosional features. The

polyhydrated sulfates are usually correlated to slightly

darker units. Kieserite and polyhydrated sulfates

correspond either to distinct lithologies or to distinct

degree of hydration or of freshness of the outcrops.

In case of obvious flat layers at canyon’s scale like in

Melas Chasma or Gangis Chasma, the sulfates are

observed in same range of elevation, over typically 1

km of thickness, in all parts of the canyon. The sulfates

follow the ILD stratigraphy and certain kinds of layers.

In case of more deformed layers like in Candor

Chasma [10] or in Ophir Chasma, the sulfates still

seem to follow the more complex stratigraphy.

Comparing the different canyons in term of vertical

location of the sulfates, we found no relationship

betweens the canyons even neighboring and currently

joined canyons. This might be explained either if the

sulfates units were formed previously to the

coalescence of canyons and/or if sulfates formed by

groundwater connections. Ages of layered deposits are

currently under study and will be reviewed at the time

of the meeting.

References:

[1] McCauley et al. (1978), 17, 289-327. [2] Nedell

et al. (1987), Icarus, 70, 409-441. [3] Chapman and

Tanaka (2001), JGR, 106, 10087-10100 [4] Komatsu

et al. (2004), PSS, 52, 167-187. [5] Peterson, C. (1981)

Proc. Lunar Planet. Sci., 12B, 1459-1471. [6] Malin

and Edgett (2000), Science, 290, 1927-1937 [7]

Lucchitta et al. (1994), JGR, 99, 3783-3798 [8]

Gendrin et al., (2005), Science, 307, 1587-1591 [9]

Gendrin, A. et al., LPSC 2006 abstract 1872, [10]

Mangold et al., 2006, This issue.


MÖSSBAUER SPECTRA OF SULFATES AND APPLICATIONS TO MARS. E.C. Sklute1, M.D. Dyar1, J.L. Bishop2, M.D. Lane3, P.L. King4, and E. Cloutis5. 1Dept. of Astronomy, Mount Holyoke College, South Hadley, MA, 01075; [email protected]. 2SETI Institute/NASA-Ames Research Center, Mountain View, CA, 3Planetary Science Institute, Tucson, AZ, 4Univ. of Western Ontario, Canada, 5Univ. of Winnipeg, Canada.

Introduction: Given the increasingly-apparent

importance of sulfate minerals on Mars, it has become critical to collect analog Mössbauer spectra of the many different mineral species (and intermediate com-positions) in the sulfate minerals groups. Because Mössbauer spectra are quite temperature-dependent, these must be collected at Mars analog temperatures. Unfortunately, almost no comparative data exist in the literature for these mineral groups. Furthermore, Mössbauer spectra of sulfates (and especially, silicate-sulfate mixtures) may be significantly affected by dif-ferential recoil-free fraction (f) effects. Here we report progress on collection of 4-293K Mössbauer spectra of a broad selection of minerals in the various sulfate groups. Our goal is to characterize their Mössbauer parameters, isomer shift (IS) and quadrupole splitting (QS) over a broad temperature range, and to determine f values that will facilitate correct interpretation of area ratios in Mossbauer spectra of sulfate minerals. All spectra and data files collected to date may be viewed at http://www.mtholyoke.edu/courses/mdyar/database/. These samples are also part of a larger study of visible-IR reflectance and mid-IR emittance spectra.

Samples: Minerals for this study were chosen from Dana groups 2, 6, 12, 28-32 and 76, and acquired from the NMNH, HMM, and mineral dealers. Miner-als were carefully handpicked to permit analyses of

single phases, and XRD was used to confirm phase identifications immediately prior to acquisition of re-flectance spectra. Although monitored, humidity was not controlled during our Mössbauer experiments, and we expect that phase changes my have occurred in some phases, particularly those with varying hydration states. Work is in progress to evaluate those changes.

Methods: Mössbauer spectra were collected at Mount Holyoke College over the temperature range from 4-293K using a closed-cycle helium cryostat.

Results: Mössbauer spectra of sulfates follow dif-ferent rules than those for silicates and oxides, but display consistent parameters representing varying permutations on the steric configurations of SO4 tetra-hedra. Most of the laboratory spectra contain multiple doublets or quadrupole splitting distributions reflecting multiple populations of site geometries, though it is doubtful that these could be resolved in MER data.

Implications for Mars Mössbauer spectroscopy: Comparison of data acquired in situ on Mars to terres-trial laboratory spectra requires use of 293K isomer shift and Mars surface temperature quadrupole split-ting data, as well as simplified fits (e.g. only doublets rather than multiple components). More data on addi-tional sulfates at variable temperatures are needed be-fore mineral identifications based on Mössbauer pa-rameters in MER results can be properly interpreted.

Table 1. Room temperature Mössbauer parameters for paramagnetic doublets in selected sulfates (in mm/s) oct Fe2+ oct Fe2+ oct Fe2+ oct Fe2+ or oct Fe3+ tet Fe2+

IS QS IS QS IS QS IS QS IS QS IS QStochilinite 1.17 2.78 0.45 0.50 0.19 0.36mackinawite* 0.48 1.28 0.20 0.50yavapaiite 0.48 0.31 römerite 1.29 3.31 1.29 2.78 0.44 0.33 0.16 0.60szomolnokite 1.29 2.74 0.55 0.38 0.23 0.69rozenite 1.27 3.33 0.37 1.15 0.20 0.48chalcanthite 1.30 2.88 1.26 2.32 0.26 0.76 0.10 0.51halotrichite 1.30 3.31 1.28 2.77 0.46 0.37 0.13 0.50kornelite 1.32 1.62 1.18 1.57 0.47 0.45 0.21 0.67coquimbite 0.45 0.08 0.16 0.66voltaite 1.34 1.62 1.20 1.58 0.47 0.37 0.14 0.61jarosite 0.38 1.23 ferricopiapite 0.38 1.18 0.42 0.40 0.43 0.77sideronatrite 0.42 1.15 fibroferrite 0.42 0.96 0.41 0.52 botryogen 1.30 1.74 0.42 1.18 0.40 1.64 0.08 0.52

*spectrum also contains sextets


PHOTOGRAPHIC EVIDENCE FOR EXHUMATION OF LIGHT-TONED DEPOSITS FROM THE WALLS OF VALLES MARINERIS. M. R. Smith, D. R. Montgomery, A. R. Gillespie, S. E. Wood and H. M. Greenberg. Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195

The origin, age, and method of deposition of the light-toned layered deposits (LLD) found within Valles Marineris have been debated since their discov-ery by the Viking spacecraft in the late 1970’s. Some have argued that the deposits lie unconformably on the existing topography within the pre-existing chasmata and post-date their formation [1,2], while others found that evidence shows light-toned material being ex-humed from the chasmata walls, suggesting that the light-toned deposits pre-date the chasmata formation [3-5]. In this study, we find significant visual evi-dence, as determined from analysis of high-resolution (~3 m/pixel) narrow-angle MOC images (Fig. 2) that exhibit exhumation of light-toned deposits from be-neath darker-toned, blocky material, which has been interpreted to be basalt flows of Hesperian Age [6]. This implies that the LLDs would be dated to Noa-chian age, far older than previously thought. As shown in Fig. 1, we see widespread evidence of such exhumation thoughout the extent of the valley system. Our work, combined with prior work of others [3-5], suggest widespread burial of the LLDs beneath the surrounding lava flows.

References: [1] Lucchitta B.K. (2001) Lunar Planet Sci. XXXII, 1359. [2] Chapman M.G. and Ta-naka K.L. (2001) JGR, 106, 10087-10100. [3] Malin M.C. and Edgett K.S. (2000) Science, 290, 1927-1937. [4] Catling D.C. et.al. (2006) Icarus, 181, 26-51. [5] Montgomery D.R. and Gillespie A. (2005) Geology, 33, 625-628. [6] Scott D.H. and Carr M.H. (1978) USGS Misc. Inv. Series., Map Series I-1083.

Figure 1. Context image for Fig. 2 along with loca-tions of other contacts in this study and those found by additional researchers. Shows the regional extent of evidence for exhumation of LLDs from beneath younger basalt flows.

Figure 2. Portions of narrow-angle MOC images showing dark-toned materials (interpreted as basalt flows) covering light-toned material. White arrows indicate contacts between dark and light material. (a) E1700753, (b) R1101206, (c) R1103842, (d) E2001074.


OVERVIEW OF THE PHOENIX MARS LANDER MISSION. P. H. Smith1, 1Lunarand Planetary Lab, University of Arizona, Tucson, AZ 85721, [email protected].

Introduction: The Phoenix lander isthe next mission to study the surface ofMars in situ. By studying the active watercycles in the polar region, it complementsthe Mars Exploration Rovers that look atthe ancient history of Mars contained inthe solid rocks. Lacking mobility, Phoenixexplores the subsurface to the north of thelander, studying the mineralogy andchemistry of the soils and ice.

Scientific Objectives, Phoenix Followsthe Water: The Phoenix mission targetsthe northern plains between 65 and 72 N.High-resolution images from the Mars Or-biter Camera on the Mars Global Surveyorspacecraft show a “basketball-like” textureon the surface with low hummocks spaced10’s of meters apart; polygonal terrain, orpatterned ground, is also common. Thesegeologic features may indicate the expan-sion and contraction of the permafrost [1].

Science goal #1: Study the history ofwater in all its phases. The circumpolarplains are active and hold clues to the cycleof water transport on Mars. Orbiter meas-urements show large seasonal variations inthe atmospheric humidity and CO2 frostblanketing the winter surface.

Quantifying the volatile inventorylocked into the arctic soils and the waterchemistry of wet soils, even at one loca-tion, is a giant step toward modeling theweather processes and climate history ofMars [2].

Liquid water changes the soil chemistryin characteristic ways. Obliquity wanderand precession are known to strongly in-fluence the climate on time scales of50,000 years or more. Does the water icemelt and wet the overlying soil on cyclescommensurate with orbital dynamics?

Science goal #2: Search for evidence ofa habitable zone. Microbial colonies cansurvive in a dormant state for extremelylong periods of time. Recent work [3]shows that as water ice melts onto soilcrystals at temperatures as cold as –20 Cmicrobes are activated and are able tosearch for food. As temperatures increase,growth and reproduction begin. Instru-ments on the Phoenix lander receive sam-

ples of this biological paydirt and test forsignatures related to biology.

Baseline Mission: After the initial as-sessment of the landing site by the scienceteam, the primary science phase of themission begins with the collection of sur-face samples. Two major science instru-ments receive and analyze the samples.The first is the thermal evolved gas ana-lyzer (TEGA). A sample is delivered to ahopper that feeds a small amount of soilinto a tiny oven, which is sealed andheated slowly to temperatures approaching1000 C. The heater power profile neces-sary to maintain a constant temperaturegradient contains peaks and valleys thatindicate phase transitions. For instance,ice will show a feature at its melting pointof 0 C and jarosite has strong endoenthal-pic transitions at 670 and 950K [4].

Gases driven from the sample are com-bined with a carrier gas and piped to amass spectrometer. The spectra of thegases change as a function of release tem-perature. Isotope ratios for H, O, C, and Nas well as heavier gases like Ar and Xeprovide scientific clues to the origin of thevolatiles.

The second instrument provides a mi-croscopic, electro-chemical, and conduc-tivity assessment (MECA) of the soils.Microscopic examination of tiny grains(less than 200 microns diameter) givesclues to the emplacement process: aeolian,lacustrine, or fluvial. A probe on the RAscoop measures the electrical and thermalconductivity of the soil.

The MECA wet chemistry laboratoryaccepts small samples into a warm beaker,and water is added to the soil while stir-ring. Special chemical sensors return dataconcerning the water chemistry including:the salt content and its composition, theacidity, and the trace mineral concentra-tion.

References: [1] Boynton, W.V. et al.(2002) Science 297, 81. [2] Smith, M. D.(2002) JGR 107, 5115. [3] Jakosky, B. M.(2003) Astrobiology 3, 343-350. [4] Ming,D.W., et al. (1996) LPSC XXVII, 883.


EXPERIMENTAL STUDIES OF JAROSITE AND ALUNITE AT HYDROTHERMAL CONDITIONS. R.E. Stoffregen , AWK Consulting Engineers, Inc., 10 Duff Road, Suite 304, Pittsburgh, Penn-sylvania, 15218, [email protected].

Introduction: The minerals jarosite

(KFe3(SO4)2(OH)6, alunite (KAl3(SO4)2(OH)6) and their sodium analogs have been studied in a variety of hydrothermal experiments over a temperature range of 100 to 450°C. Due to mineral stability and reaction rate considerations, experiments on jarosite were con-ducted mainly in the temperature range of 100-250°C, and those for alunite from 250-450°C. These experi-ments have defined the stability field of jarosite rela-tive to hematite [1]; determined mineral-fluid Na-K distribution coefficients and provided constraints on the mixing behavior along the jarosite-natrojarosite [1] and alunite-natroalunite [2] binaries; measured the fractionation of oxygen isotopes between water and the sulfate and hyroxyl sites in alunite, and the D-H fractionation between water and alunite [3]; and pro-vided reconnaissance information on these mineral-water isotope fractionation factors for jarosite [4]. In addition, the experiments provide rates of alkali and isotope exchange between these minerals and co-existing aqueous solutions that can be extrapolated to lower temperatures with some confidence [1,5].

Jarosite Stability: Jarosite is stable relative to hematite below a log m H2SO4 of –0.35 ± 0.5 at 250° C and –0.58 ± 0.12 at 200°C (corresponding to m H2SO4 of 0.45 and 0.26). Natrojarosite could not be produced from hematite at 250°C, but was stable be-low a log m H2SO4 of –0.17 ± 0.08 at 200°C (corre-sponding to a m H2SO4 of 0.68). These extreme sulfu-ric acid concentrations required for jarosite stability are consistent with the rarity of jarosite in hydrother-mal environments on earth. Decreasing temperature increases the jarosite stability field, consistent with the common occurrence of jarosite in terrestrial surface environments where pyrite serves as a source of sulfu-ric acid during weathering.

Alkali Exchange and Mixing: The distribution coefficient for the exchange reaction

(1) jarosite + Na+ = natrojarosite + K+

is -4.9 at 150°C, -3.7 at 200°C, and -3.1 at 250°C, and values for the analogous alunite-natroalunite reaction are: -2.56 at 250°C, -1.73 at 350°C and –0.99 at 450°C. These values indicate that partitioning of al-kalis is similar for jarosite and alunite, and that in-creasing temperature favors the sodium end-member for both phases.

Experimental results suggest that jarosite-natrojarosite can be modeled as an ideal solid solution at 200°C. Increasing departures from ideality with decreasing temperature are not precluded by the ex-perimental data, but a solvus in the system jarosite-natrojarosite is considered unlikely. In contrast, the alunite-natroalunite binary shows a substantial depar-ture from ideality that increases with decreasing tem-perature from 450 to 250°C. An asymmetric solvus is considered likely with decreasing temperature.

Isotope Exchange: Alunite-water oxygen and hy-drogen isotope fractionations were determined in cou-ple alkali and isotope exchange experiments. Results were used to develop an intra-mineral geothermometer based on oxygen isotope fractionation between the alunite sulfate and hydroxyl sites. Reconnaissance jarosite-water isotope fractionation experiments were also conducted, but their interpretation was compli-cated by apparent non-equilibirum effects.

Reaction rates: The experimentally determined rate of jarosite-fluid alkali exchange over the tempera-ture range of 200-108°C was

log t½ = -14.38 + 6.28 (1000/T (K)),

where t½ is equal to the time required for 50% ex-change, in days. When extrapolated to 25°C, this equation suggests that jarosite will rapidly equilibrate (at geologic times scales) with co-existing fluids even at earth-surface conditions. This should be taken into consideration when studying the stable isotope sys-tematics of jarosite, or using it for K-Ar dating. Ex-perimentally determined alunite-fluid exchange rates are roughly three orders of magnitude slower than those for jarosite, which suggests that alunite, unless it is fine-grained, will not re-equilibrate at surface condi-tions.

References: [1] Stoffregen, R.E. (1993) GCA, 57, 2417-2429. [2] Stoffregen, R.E. and Cygan, G.L. (1990) Am. Min., 75, 209-220. [3] Stoffregen, R.E. et al. (1994) GCA, 58, 903-916. [4] Rye, R.O. and Stof-fregen, R.E. (1995) Econ. Geol, 90, 2336-2342. [5] Stoffregen, R.E. et al. (1994) GCA, 58, 917-929.


DETECTION OF JAROSITE AND ALUNITE WITH HYPERSPECTRAL IMAGING: PROSPECTS FOR DETERMINING THEIR ORIGIN ON MARS USING ORBITAL SENSORS. G. A. Swayze1, G. A. Desbor-ough1, R. N. Clark1, R. O. Rye2, R. E. Stoffregen3, K. S. Smith1, and H. A. Lowers1, 1 U.S. Geological Survey, MS964, Box 25046 DFC, Denver, CO 80225, [email protected], 2 U.S. Geological Survey, MS963, Box 25046 DFC, Denver, CO 80225, 3 AWK Consulting Engineers, Inc., 10 Duff Rd., Suite 304, Pittsburgh, PA, 15218.

Recent identification of jarosite at Meridiani Planum [1]

has generated intense interest because its mode of formation may constrain past conditions on the planet. The small foot-print (18 m) of the Mars Reconnaissance Orbiter CRISM spectrometer may allow recognition and mapping of jarosite and other sulfate minerals from orbit in the coming months on a planetary scale. Alunite is commonly associated with jarosite in terrestrial deposits [2, 3] and has been recognized in Hawaiian basalts [4] used as analogs for Martian volcanic rocks. Given this, it is likely that CRISM scientists will eventually find alunite on the Martian surface. Alunite, like jarosite, may potentially form on Mars in a number of modes ranging from high-temperature environments associated with magmatic fluids, to lacustrine or supergene environments (formed possibly from CO2-facilitated oxidation [5] of Fe2+ in sulfides and H2S in aqueous fluids).

Determining the origin of alunite and jarosite in terres-trial environments can be accomplished using stable iso-topes; however, this method requires laboratory analyses [2, 3]. A spectroscopic tool that could be used from orbit to distinguish between such environments may prove valuable in selecting future landing sites with the highest potential for preserving evidence of past life.

Jarosite and alunite have detectable spectral features in the 1.3 to 2.5 micron region that can be used to determine their Na and K composition in the laboratory [6]. Reflec-tance spectra of jarosites and alunites synthesized at different temperatures (95 to 200C and 150 to 450C respectively) show OH-related vibrational absorptions that become narrow and more intense in the higher-temperature samples. A pos-sible explanation for this behavior is the protonation of hy-droxyls that charge balance Fe and Al deficiencies in low-temperature synthetic jarosite and alunite. Replacement by H2O of one or more of the three hydroxyls, which are each hydrogen bonded to an apical sulfate oxygen, disrupts strong vibrational coupling, thereby weakening the spectral absorp-tions. When these samples are heated, the protonated hy-droxyls are liberated as “excess water,” and recrystallization produces fully hydroxylated crystals with intense spectral features that resemble those of natural high-temperature jarosite and alunite. Synthetic hydronium jarosite and alunite spectrally resemble low-temperature synthetic Fe-deficient jarosite and Al-deficient alunite, respectively. Pro-ton transfer from the H3O+ ion to the OH site in synthetic hydronium jarosite increases chemical disorder on its OH sites [7], also resulting in muted spectral features. This also applies to hydronium alunite.

Temperature-dependent spectral variations have been observed for 70 natural alunite samples formed at tempera-tures ranging from 20 to 400C. Spectral observations of 19 natural jarosite samples showed only a temperature depend-ency for a recently formed stalactitic hydronium-bearing jarosite from Iron Mountain, California. This jarosite had broad, weak absorptions characteristic of the low-temperature synthetic jarosites. All the other jarosite sam-ples, including those formed in supergene environments (<80C), have narrow, intense absorptions similar to high-temperature synthetic jarosites. A likely explanation for the spectral similarity of all aged jarosites is the tendency for them to recrystallize into alkali endmembers over time. XRD analysis of 32 natural hydrothermal and supergene K- and Na-jarosites determined that intermediate compositions are absent, and instead, mixtures of discrete K and Na end-members typify most samples [8]. The recrystallization likely results in loss of protonated hydroxyls in the lattice that are diagnostic of formation temperatures. This is not the case for natural alunite, which apparently does not undergo extensive recrystallization over time.

If alunite is exposed on the surface of Mars over a suffi-ciently large area, then the CRISM spectrometer should de-tect it and determine its K and Na composition as has been shown using AVIRIS spectra collected over Cuprite, Nevada [9]. This spectrothermometer also could be used to differen-tiate between alunite in high-temperature, relict, acid-sulfate hydrothermal systems and low-temperature, acid-saline lacustrine sediments. Selection of Martian landing sites to seek evidence of past life could be guided by sulfate altera-tion minerals. Which has the greatest probability of preserv-ing evidence of life, alunite-bearing, low-temperature super-gene and lacustrine rocks or alunite-bearing, hydrothermally- altered rocks? This spectrothermometer and others like it may be useful tools for selecting interesting landing sites from Mars orbit.

References: [1] Klinglehoffer et al. (2004) Science,

306, 1740. [2] Rye et al. (1992) EcoGeol, 87, 225. [3] Rye and Alpers (1997) USGS OFR97-88. [4] Wolfe et al. (1997) USGS Prof Paper 1557. [5] Papike et al. (2006) GCA, 70, 1309. [6] Bishop and Murad (2005) AmMin, 90, 1100. [7] Grohol et al. (2003) PhysRevB, 67, 064401. [8] Desborough et al. (2006) ICARD, 458. [9] Swayze et al. (2003), JGR, 108(9), 5105.


CHEMICAL DIVIDES AND VARIATION IN MARTIAN SALINE MINERALOGY. N. J. Tosca1 and S. M. McLennan1, 1Department of Geosciences, SUNY at Stony Brook, Stony Brook, NY 11794-2100 ([email protected])

Introduction: Characterization of evaporitic envi-

ronments at the martian surface remains a priority for Mars exploration. Saline mineral assemblages, now identified and characterized by missions such as MER and MEx, can retain detailed chemical characteristics about their parent fluids, potentially yielding properties such as pH, oxidation state, anion content (and hence atmospheric volatile input), and dominant weathering processes. The interplay of this information is com-plex, but on Earth, the “chemical divide” concept has been used with much success in unraveling these prop-erties. However, the fundamental differences in sur-face geochemistry between Earth and Mars prevent the direct use of the terrestrial chemical divide system and its predictive capabilities. Accordingly, we have sug-gested a new chemical divide system for the martian surface that predicts evaporite assemblages identified in SNC-meteorites, ancient evaporites identified by the MER mission, as well as Mars Express OMEGA [1].

Dilute fluid chemistry and chemical divides at the martian surface: The mineralogy of a saline as-semblage is already pre-determined at the time the dilute fluid has acquired solute and evaporation has begun. Indeed, understanding possible variation in martian fluid chemistry translates to understanding variation in saline minerals across the planet, the fre-quency of their occurrence, and modes and timing of their formation.

During evaporation, the precipitation of each saline mineral will create a turning point in the outcome of the entire saline assemblage. This turning point can be referred to as a chemical divide – it ocurs when the precipitating mineral consumes two chemical compo-nents in a different ratio than their abundance in the fluid.

One of the most important controls on solute ac-quisition of any surfacial fluid is the chemical weather-ing of crustal materials. On Mars, where the crust is almost entirely basaltic in composition, fluids weather-ing the crust will be dominated by Mg, SiO2(aq), Ca and, under acidic conditions, Fe. At the martian sur-face, chemical weathering reactions will be driven by acid input and the consumption of acidity by mineral dissolution will compete with this process to increase pH levels. The variation in pH will in turn control the anion balance, which may be imposed on the system by the atmosphere. For Mars, SO4, HCO3 and Cl are the most important anions to the system, controlled mainly by volcanic input and a high pCO2 atmosphere.

Taken together, the cation ratio present in surficial fluids will be determined by basaltic weathering and

the inter-dependence of pH, HCO3, SO4 and Cl content serves as the major source of variation in anion com-position of martian surface waters.

Geochemical modeling of varying solution compo-sitions according to the model above permits us to identify the major saline precipitates and resulting as-semblages. By constructing a detailed chemical divide scheme for this system, the possible products and their modes of formation under acidic conditions are identi-fied and can be used for predictive capabilities.

Application to current and future mineralogical data: The chemical divide system described above predicts the occurrence of the saline assemblages iden-tified in the SNC meteorites, and specifically, in the Nakhla meteorite (representing the most advanced stage of evaporation). The distinct chemistry of these parent fluids corresponds to a mixed, sulfate-carbonate geochemical environment. The implications of the SNC mineralogy and their formation pathways points to slow Fe oxidation, only mildly acidic pH and HCO3 input, possibly confined to the subsurface where at-mospheric cutoff allows pH to increase.

The geochemical environment giving rise to the sa-line minerals identified by the MER rover resides on the opposite end of the spectrum from the SNC mixed carbonate-sulfate environment. Acidity in the parent fluids need only to overcome carbonate alkalinity to result in an entirely sulfate-dominated mineral assem-blage. Low pH may have been attained by any combi-nation of acid volatile input, evaporation, Fe oxidation and hydrolysis, or sulfate-mineral recycling. This chemistry may have been attained by constant expo-sure to the atmosphere and high acidic-volatile input. Such a geochemical environment is also consistent with OMEGA-derived sulfate mineralogy. In compar-ing these two environments, it is clear from the system of chemical divides that a common fluid type simply buffered to varying degrees by chemical weathering can explain the variation observed in martian saline assemblages.

Perhaps more importantly, our chemical divide sys-tem shows that at least three factors are responsible for the unique saline mineralogy observed at the surface of Mars: (1) acidic environments controlled by SO4, HCO3 and Cl input, (2) increased mobility and con-centration of Fe in aqueous systems, and (3) dilute water chemistry dominated by the weathering of a ba-saltic regolith.

References: [1] N. J. Tosca and S. M. McLennan (2006) EPSL, 241, 21-31.


SULFATE-BEARING MINERALS IN THE MARTIAN METEORITES. A. H. Treiman, Lunar & Planetary Institute, 3600 Bay Area Blvd., Houston TX 77058 <treiman{at}lpi.usra.edu>.

Introduction: The Martian meteorites contain Martian, water-deposited sulfate-bearing materials [1,2] – direct positive evidence of sulfate and other volatiles in the Martian hydrosphere. These materials are invaluable for understanding Martian chemical hydrology, as they can be characterized for structure, chemistry, and isotope ratios using the most sophisti-cated instruments on Earth. Commonly, Martian sul-fatic materials are difficult to distinguish from terres-trial deposits and alterations. In addition, the environ-ments and processes of terrestrial alteration are under active study [3,4], and alteration features at the sub-micron level can be ambiguous [5,6]. Despite these issues, interest in sulfates in Martian meteorites is strong, benefiting from new instrumental methods, and synergy with results from spacecraft at Mars.

Nakhlites: The nakhlites are augite-rich cumulate igneous rocks, which contain clay-rich alteration mate-rial (iddingsite), Fe-Mn carbonate, halite, and Ca sul-fate (anhydrite and/or gypsum) [2]. Several apparently contain jarosite (by EMP analyses [7,8,9]). These ma-terials were deposited by aqueous solutions in void-space produced by dissolution of olivine. Deposition of carbonate and sulfate may precede, and overlap with, deposition of clay [10]. Nakhla also contains Mg-sulfate along cracks [11].

Stable isotopic data show that these minerals are Martian, and that their source was in chemical com-munication with the Martian atmosphere. D of the iddingsite ranges up to ~+750‰ [12], consistent with admixture of atmospheric H. 17O of the iddingsite, carbonate, sulfate are +0.6 – +1.4‰ [13-15], much higher than the anhydrous silicates, and ascribed to the Martian atmosphere. Sulfur from the sulfates shows strong non-mass-dependent fractionations suggestive of atmospheric photochemical reactions [16]. These isotope data suggest that the water and solutes in-volved in nakhlite alteration were derived from (and processed through) the Martian atmosphere, and had limited prior interactions with Martian igneous rocks.

EETA79001: Shergottite EETA 79001 contains the purest known samples of Martian atmosphere gases [17], and has a rich assemblage of alteration salts: Ca-sulfate, S-Cl-bearing aluminosilicate (poorly defined), calcite, Mg-phosphate, and a Pb-S-Cr mineral [18,19]. The last may be Pb2O(SO4,CrO4) [20]. The origin of these salts is not clear. Some of the carbonate is terres-trial by 14C [21], while 13C and 18O suggest an extra-terrestrial source [22]. The textures are (to me) not conclusive of a Martian origin [18,19].

Other Martians: Little is known about Martian sulfate alteration materials in other meteorites. ALH 84001 contains abundant carbonate minerals, but little or no sulfate [23]. Chassigny contains Ca-sulfate and Ca-Mg carbonates (with traces of Cl and P), along grain boundaries [24]. Shergotty contains Ca sulfate, halite, an Mg sulfate, and phyllosilicates along frac-tures [25]. Shergottite QUE 94201 contains a rich as-semblage of Ca-sulfate, Fe-sulfate, K-Fe sulfate (jarosite?), Mg-phosphate, silica, and S-Cl-bearing aluminosilicate. Their textures, however, are consistent with a terrestrial origin [26]. ALH77005 contains aqueous replacements of olivine and chromite [27]; the latter are rich in K, S, and P and may include jarosite ([28], K. Kuebler, pers. comm.).

Conclusion: Aqueous alteration materials in the Martian meteorites contain sulfate minerals: anhydrite and/or gypsum, Mg-sulfate, jarosite (?), and S-bearing aluminosilicates (clays?). These minerals can provide crucial information on Martian aqueous processes and chemistry, if they can be proven to be Martian.

References: [1] Gooding JG (1992) Icarus 99 28-41. [2] Bridges JC et al. (2001) Space Sci. Rev. 96, 365-392. [3] Harvey RP et al. (2006) LPS XXXVII, Abstr. #1044. [4] Kopp RE & Humayan M (2003) GCA 67, 3247-3256. [5] McKay D et al. (1996) Sci-ence 273, 924-930. [6] Bradley et al. (1997) Nature 390, 454-455. [7] Noguchi T et al. (2003) NIPR Symp. Ant. Met. [8] Stopar JD et al. (2005) LPS XXXVI, Abstr. #1547. [9] Herd CDK (2006) Met. Planet. Sci. 41, Abstr. #5027. [10] Pauli E & Vicenzi EP (2004) Met. Planet. Sci. 39, Abstr. #5191. [11] Gooding JG et al. (1991) Meteoritics 26, 135-143. [12] Leshin LA et al. (1996) GCA 60, 2635-2650. [13] Karlsson H et al. (1992) Science 255, 1409-1411. [14] Romanek C et al. (1998) Met. Planet. Sci. 33, 775-784. [15] Farquahr J et al. (2000) JGR 105, 11991-11997. [16] Farquhar J et al. (2001) Nature 404, 50-52. [17] Becker & Pepin (19xx) . [18] Gooding JG & Muenow DW (1986) GCA 50, 1049-1059. [19] Gooding JG et al. (1988) GCA 52, 909-916. [20] Treiman AH (1999) LPS XXX, Abstr. #1124. [21] Jull AJT et al. (1998) Science 279, 366-369. [22] Wright IP et al. (1988) GCA 52, 917-924. [23] Romanek C et al. (1995) Meteoritics 30, 567. [24] Wentworth SJ & Gooding JG (1994) Meteor-itics 29, 860-863. [25] Wentworth SJ et al. (2000) LPS XXXI, Abstr. #1888. [26] Wentworth SJ & Gooding JG (1996) LPS XXVII, 1421-1422. [27] Steele I & Smith JV (1984) Meteoritics 19, 121-133. [28] Gooding JG (1984) LPS XV, 310-311.


RATES AND MODES OF HYDRATION IN Mg- AND Ca-SULFATES ON MARS. D. T. Vaniman and S. J. Chipera, Hydrology, Geology and Geochemistry, Group EES-6, MS D462, Los Alamos National Laboratory, Los Alamos NM, 87545 ([email protected]).

Introduction: Many salts and salt hydrates may

be present on Mars. Here we consider the simple sul-fate salts MgSO4.nH2O (n=1 to 7, but n of 11 or 12 may be possible) and CaSO4.nH2O (n=0 to 2). Ex-periments at low pH2O indicate that if derived from forms with higher values of n, at least some Mg-sulfates with low values of n are amorphous [1]. How-ever, more hydrous forms such as epsomite (n=7) may be stable at higher latitudes where near-surface water ice persists [2]. Spectral data indicate that near-equatorial Ca-sulfate forms are hydrated, but do not constrain the value of n [3]. Gypsum may be common at all latitudes, but high-temperture events (volcanism, impact, metamorphism) may produce less hydrated forms such as bassanite (n~0.5) or anhydrite (n=0). Even at modestly elevated temperature (297 K), bas-sanite forms from gypsum with prolonged exposure to Mars-like pH2O (~100 hours at pH2O of ~0.7 Pa;[4]). Impact distribution or eolian transport can move sul-fates from zones with one persistent hydration state to zones where they may either desiccate or hydrate.

Hydration Rates and Products: Figure 1 com-pares hydration of three salts at 271 K – kieserite (no=1), amorphous Mg-sulfate (no=1.2), and desiccated bassanite (no=0.06). Hydration was at 100% RH con-trolled by water ice. Kieserite and the amorphous Mg-sulfate pass through states of hydration equivalent to several different phases (e.g., sanderite, starkeyite, pentahydrite, hexahydrite), but the hydration curves show no inflection at these hydration states, indicating that intermediate phases either do not form or they present no energy barriers to further hydration. The curves do however have pronounced inflection where eposomite is fully formed (n=7); epsomite persists for ~7,000 hours before deliquescence begins. In contrast, the desiccated bassanite hydrates rapidly to n~0.6, where the hydration rate slows before accelerating again to the point where gypsum is fully formed (n=2).

Figure 2 shows hydration of the same three desic-cated salts at 243 K with RH controlled at 100% by water ice. There are no significant inflections in the Mg-sulfate hydration curves up to n=7. X-ray diffrac-tion shows early formation of hexahydrite with in-growth of epsomite; less hydrous forms do not appear. Hydration of amorphous starting material is signifi-cantly more rapid than kieserite. The kieserite starting material shows a strong decrease in hydration rate at n=7 but does not plateau at n=7. Beyond ~4000 hours both Mg-sulfates show a slow increase in weight; it is

yet to be determined whether these second-stage hy-dration curves will lead to crystalline forms of higher hydration (n= 11 or 12); at this low temperature (27 degrees below the freezing point of saturated Mg-sulfate solution) deliquescence will not occur. Desic-cated bassanite hydrates to n~0.6 within 200 hours, but at 3,000 hours there is yet no indication of further hy-dration toward gypsum (experiment in progress). At 243 K hydration can occur in less than one Mars year, but preliminary data indicate that this is not the case at 190 K. Further studies will evaluate whether desic-cated forms migrated to higher latitudes can rehydrate within seasonal or obliquity timescales.

Figure 1: desiccated samples of amorphous MgSO4,kieserite, and bassanite rehydrated in vaporcommunication with water ice at 271 K

kiese

rite(n o

=1)

bassanite (n o=0.06)

amorp

hous (n o

=1.2)

1 10 100 103 104 1051

10

100

103

n=7

n=2

time (hours)

wt%

gain

Mar

sye

ar

n=0.6

deliq

uesc

ence

Figure 2: desiccated samples of amorphous MgSO4,kieserite, and bassanite rehydrated in vaporcommunication with water ice at 243 K

1

10

100

103

wt%

gain

1 10 100 103 104 105time (hours)

Mar

sye

ar

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rite(n o=

1)

bassa

nite(n o

=0.06)

amorphous (n o=1.2)

n=7

n=0.6

increase without

deliquescence

References: [1] Vaniman D. T. et al. (2004) Na-

ture, 431, 663-665. [2] Zolotov M. Yu. (1989) LPS XX, 1257-1258. [3] Gendrin A. et al. (2005) Science, 307, 1587-1591. [4] Vaniman D. T. and Chipera S. J. (in press) American Mineralogist.


OLIVINE AND SECONDARY SULFATE MINERALS IN CHASSIGNY AND OTHER MARS METEORITES: COMPARISON WITH INCIPIENT WEATHERING OF TERRESTRIAL DUNITIC AND BASALTIC OLIVINE. M. A. Velbel1, S. J. Wentworth2, and J. M. Ranck3, 1Department of Geological Sciences, 206 Natural Science Building, Michigan State University, East Lansing, MI 48824-1115 ([email protected]), 2ESCG, Mail Code JE23, Johnson Space Center, Houston, TX 77058 ([email protected]), 3Affiliation URS Corporation-North Carolina, 1600 Perimeter Park Drive, Morrisville, NC 27560 ([email protected]).

Introduction: Sulfates have been reported from

several Mars meteorite falls [1] encompassing a vari-ety of igneous rock types, including Chassigny (dunite) [1,2], Nakhla (clinopyroxenite) [1,3], and Shergotty (basalt) [1], as well as in a number of Mars meteorite finds [1,4,5]. The Mars Exploration Rovers have revealed the importance of sulfates in Mars’ sur-face materials. This contribution describes the occur-rence of sulfate minerals in Chassigny and several oli-vine-rich terrestrial rocks that might serve as analogs for the onset of aqueous alteration in Chassigny.

Previous work: Olivine and sulfates in dunite: Chassigny. Wentworth and others [1] reported various Ca-sulfates on exposed olivine grain-boundary fracture surfaces in the Martian dunite Chassigny. In addition to occurrences of individual evaporite minerals, some disk-shaped masses occur with non-porous Ca-sulfate in the center, surrounded by microgranular/porous (devolatilized?) Ca-carbonate [1].

Silicates and sulfates in Nakhla and Shergotty. Wentworth et al. [1] reported striated (corroded) Ca-sulfate in Nakhla, superposed in some instances by halite [6]. They also reported several occurrences of evaporites in Shergotty [1,6], in which corroded Ca-sulfate occurs on an unmodified silicate surfaces.

Methods: Samples of Chassigny and several ter-restrial olivine-rich rocks were fragmented exposing natural fracture surfaces, coated with Au or Au-Pd, and examined by conventional and field-emission-gun (FEG-) scanning electron microscopy (SEM).

Results: SEM images reveal local, fracture-filling disk-shaped patches of microgranular or porous mate-rial similar to the porous carbonate/sulfate patches previously reported from Mars meteorites, in ostensi-bly “fresh” (mineral-teaching-collection) dunite from North Carolina. Olivine in the terrestrial dunite is lo-cally corroded by typical anhedral, funnel-shaped etch pits identical to those observed elsewhere [7,8]. In some instances, the etch pits are directly associated with small amounts of cornflake-textured clay-like material; much similar material occurs unrelated to etch pits in this and other samples. In neither Martian nor terrestrial dunite observed to date are secondary non-clay products (sulfates or carbonates) associated with olivine etching/corrosion features (e.g., etch pits, mammilary surfaces). Furthermore, while possible

corrosion textures have been observed in other Mars meteorites [1], such corrosion features have not been observed to date in Chassigny. Anhedral olivine etch pits like those common on terrestrially weathered oli-vines [7,8] are observed in other parts of the “fresh” teaching-collection terrestrial dunite, but not in direct association with fracture-filling products.

Discussion: Olivine etch pits on the “fresh” terres-trial dunite indicate either pre-weathering aqueous alteration of olivine, or that small amounts of weather-ing affected the sample despite its fresh appearance. Sulfate is likely not the original form of S in dunite. Any sulfates in dunite may have formed by oxidation of primary sulfide minerals. However, sulfide oxida-tion in the presence of water usually forms sulfuric acid, suggesting that sulfate formation by this process should be accompanied by corrosion features typical of acid dissolution of olivine. The lack of direct asso-ciation of secondary evaporites with corrosion features on primary olivine in the terrestrial analog dunite sug-gests that, in these cases, olivine exposed at grain-boundary and grain-traversing fractures was a passive substrate for the deposition of the evaporites, and that the olivine did not react directly or locally with the solutions from which the evaporites precipitated. It remains to be established whether sulfate introduced into olivine fractures is indigenous to the parent rock or transported into the fractures from other regolith materials. The lack of association between olivine corrosion and secondary sulfates favors the latter. If so, occurrences of sulfate minerals in Mars meteorites may be related to sulfate-bearing surface- and groundwaters inferred to have been important in Mars’ surface and near-surface aqueous environments.

References: [1] Wentworth S. J. et al. (2005) Icarus, 174, 382-395. [2] Wentworth S. J. and Good-ing J. L. (1994) Meteoritics, 29, 860-863. [3] Gooding J. L. et al. (1991) Meteoritics, 26, 135-143. [4] Good-ing J. L. et al. (1988) GCA, 52, 909-915. [5] Gooding J. L. (1992) Icarus, 99, 28-41. LPS XXVII, 1344–1345. [6] Wentworth S. J. et al. (2001) LPS XXXII, Abstract #2108. [7] Velbel M. A. (1993) Amer. Mineral., 78, 408-417. [8] Velbel M. A. (2006) LPS XXXVII, Ab-stract #1807.


HYDRATION STATE OF MAGNESIUM SULFATES ON MARS. Alian Wang, John J. Freeman, Bradley L. Jolliff, Department of Earth & Planetary Sciences and McDonnell Center for the Space Sciences, Washington Uni-versity, St. Louis, MO, 63130 ([email protected])

Introduction: Mg-sulfate has been found on Mars

by the Mars Exploration Rovers (MER) [1,2,3] and by OMEGA/Mars Express [4,5,6]. The MER data do not directly measure the hydration state of these Mg-sulfates; however, OMEGA spectra suggest kieserite (MgSO4·H2O) and “Polyhydrated sulfates.” Knowl-edge of the hydration state of Mg-sulfates currently at or near the surface of Mars is important to tie these evaporate minerals with the hydrogen detected by the Neutron Spectrometer on the Mars Odyssey orbiter [7]. More importantly, their structural character (e.g., crys-tallinity) and hydration states could be crucial indica-tors for short-term and long-term hydrologic evolution on Mars. The specific mineralogy of sulfur is also sig-nificant in martian H2O and S cycles, and may play key roles in the potential for habitability.

Experiments: We have studied the stability field and phase transition pathways of hydrous Mg-sulfates

using Raman spectroscopy as the major analytical method, accompanied by mass-loss measurements, XRD, and IR spectroscopy. Eighty six samples of pure Mg-sulfates and mixtures of Mg- and Ca-sulfates were studied over 1000 hours at 10 different relative humid-ities and two temperatures, with 4 different hydration states as starting phases.

Results: Four major results were obtained from these experiments. Figure 1 shows the Raman spectra from this study [8,9,10], with hydration states ranging from anhydrous through 12 H2O, and MgSO4 in solu-tion. Fig. 2a shows Raman spectra from mixed hy-drous Mg-sulfates, which represent experimental products .

(1) Amorphous Mg-sulfate can be formed readily from epsomite and hexahydrite, but not from starkeyite or kieserite, through fast vacuum dehydration or slow dehydration under dry condition (5.5% RH). An amor-

phous structure can hold up to 3 H2O per MgSO4 molecule at 50˚C, and is stable under extremely dry (5.5% RH) conditions.

(2) Starkeyite is stable at ex-tremely dry conditions (5.5% RH) at 21˚C ≤ T ≥ 50˚C. The NIR spectral patterns of starkeyite and amorphous Mg-sulfates match the OMEGA spectrum of “Polyhydrated sulfates”.

(3) At T≤ 50º C, kieserite is not formed by either fast or slow dehy-dration of epsomite, hexahydrite, or starkeyite, but can be formed from slow dehydration of amorphous Mg-sulfates and from a mixture of hexa-hydrite and Ca-sulfate (Fig.2b).

(4) The dehydration rate of hexa-hydrite can be greatly reduced (over 10 times) when it is first mixed with Ca-sulfates of all hydration states.

References: [1]. Klingelhöfer et al., 2004, Science; [2] Haskin et al., 2005, Nature; [3] Wang et al., 2006a, JGR; [4] Bibring et al., 2005 Science; [5] Gendrin et al., 2005, Science; [6] Arvidson et al., 2005 Science, [7] Feldman et al., 2006 JGR., [8] Wang et al., 2006b, 37th LPSC; [9] Wang et al., 2006c, 37th LPSC; [10] Wang et al., GCA, in press.

Figure 1. Raman spectra of hydrous & anhydrous, crystalline and amorphous Mg-sulfates as the basis of the current study8,9,10.

Raman Shift (cm-1)

400 500 600 700 800 900 1000 1100 1200 1300

MgSO4 aqeous solution

MgSO4.4H2O Starkeyite

MgSO4.H2O Kieserite

Anhydrous MgSO4

MgSO4.6H2O Hexahydrite

MgSO4.5H2O Pentahydrite

MgSO4.2H2O Sanderite

MgSO4.3H2O

984.2

1005.0

1000.3

983.6

984.1

1022.8

1047.7

1033.8

1023.8

1052.7

MgSO4.7H2O Epsomite

MgSO4 .12H2O

982.1

*

1030Amorphous MgSO4.2H2O

Figure 2. (a) Raman spectra of Mg-sulfate mixtures; (b) 1w- & 2w- (in addition to 4w-) MgSO4 can be produced from the dehy-dration of hexahydrite, when it is first mixed with Ca-sulfates.

6w

6w

6w

Raman shift (cm-1)900 950 1000 1050 1100 1150

5w*

3w*

1w

3w* 2w*1w

3w*

1w

6W

2W

CaSO4

4W

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6W

2W

CaSO4

4W

1W


ATMOSPHERIC SULFUR CHEMISTRY ON ANCIENT MARS. K. Zahnle1 and R. M. Haberle2, 1NASA Ames Research Center, MS 245-3, Moffett Field CA 94043, [email protected] 2 NASA Ames Research Center, MS 245-3, Moffett Field CA 94043, [email protected].

Introduction: Sulfates appear to be abundant on

Mars. The ultimate source of the sulfate was probably volcanic gases [1], much as it would have been on Earth before the advent of atmospheric oxygen [2]. Isotopically fractionationed S found in martian meteor-ites confirm that at least some martian sulfate had its origin in photochemically processed atmospheric gases [3].

The chief volcanic sulfur gas on Earth is SO2. If anything, SO2 would be more dominant for Mars, whose basalts are much drier than Earth’s and hence less capable of emitting H2S. We might expect other reduced volcanic ghases –H2 and CO - to be less im-portant on Mars as well.

Ancient volcanic SO2 fluxes are estimated presum-ing that the global mean sulfate cover is 100 m thick, and that the volcanoes erupted for 0.5 Gyrs. This gives an average SO2 injection rate of 4e9 molecules/cm2/s. This is about twice the current terrestrial average.

In an oxidized atmosphere SO2 is invariably oxi-dized to SO3, which quickly hydrates to make sulfuric acid. This is SO2’s fate on Earth, and it is SO2’s fate on Mars if the volcanoes are extinct enough. But in a neutral or reduced atmosphere the source of oxygen to make SO3 from SO2 becomes an issue.

For ancient Mars, the thriving volcanoes needed to generate 100 m of sulfate greatly exceed the capacity of hydrogen escape to oxidize the atmosphere. The only real alternative is for SO2 to disproportionate, so that as some SO2 is oxidized to SO3, other SO2 is re-duced to elemental sulfur. In the limit one expects 24SO2 + photons -> 16SO3 + S8. We therefore expect that elemental sulfur would have been a significant product of atmospheric photochemistry.

Here Earth provides a reality check. Terrestrial sediments older than 2.46 Ga preserve strong signa-tures of distinctively mass fractionated sulfur [4]. The fractionations undoubtedly took place in the atmos-phere. The tricky bit is how they reached the sediments with fractionations intact. The best answer is that parti-cles of elemental sulfur fell from the sky [5]. Elemen-tal sulfur is insoluble in water and thus, while all other sulfur species dissolve together in vast salty seas, ele-mental sulfur does not. It makes its own way by its own path into the geologic record.

The photochemistry model: In order to make quantitative predictions we developed a 1D photo-chemical model.

The central fact of martian photochemistry is the O2/CO ratio. In steady state, the O2/CO ratio is de-termined by how much O2 needs to build up in the atmosphere to make the oxygen sink big enough to balance hydrogen loss to space. This means that the key question is to identify the oxygen sink. To apply a photochemical model to the redox state of ancient mar-tian atmospheres (those with more SO2, those with more CO2, or both) requires specifying the processes that govern H escape and O loss.

Our model does a good job with O2, CO, and H2O2, it underpredicts O3, and it overpredicts H2 for the current best estimates of the rate of H escape to space. In short it closely resembles all other 1D photo-chemical models [6-8]. The distinctive feature of our model is that it works by chemical reactions at the sur-face; i.e., our model presumes that hydrogen escape is directly balanced by soil oxidation. We implement this by assuming a single deposition velocity for all reac-tive gases. Currently H2O2 and O3 are the most im-portant.

Our model features an extensive sulfur photochem-istry that includes H2SO4, SO3, SO2, SO, S, S2, S3, S4, S8, OCS, HS, and H2S, and also H2SO4 and S8 aerosols. Both kinds of aerosols can precipitate.

Preliminary results indicate that the transition be-tween oxidized and reduced 6.3 mbar martian atmos-pheres begins when the SO2 source reaches 2e8 mole-cules/cm2/s (~10% of modern terrestrial levels). The onset of elemental sulfur precipitation occurs at 2e9 molecules/cm2/s, and at 1e10 (exuberant volcanoes) more than 20% of the sulfur precipitates as the ele-ment. The model also predicts that reduced sulfur gases, especially SO and SO2, would be likely to react directly with the soils at significant rates.

Preliminary results indicate that the redox state of the martian atmosphere is sensitive to pCO2, with higher pCO2 levels producing more reduced atmos-pheres. CO becomes a major gas for pCO2 > 200 mbars.

References: [1] Settle M. and Greeley R. (1979) JGR 84, 8343–8354. [2] Walker J. C. G. and Brimble-combe P. (1985) Precambrian Res. 28, 205-222. [3] Farquhar J. et al. (2000) Nature 404, 50–52. [4] Farquhar J. and Wing B. (2003) E.P.S.L. 213, 1–13. [5] Ono S. et al. (2003) E.P.S.L. 213, 15-30. [6] Nair H. et al. (1994) Icarus 111, 124-150. [7] Atreya S. and Gu H. (1994) JGR 99, 13133-13145. [8] Krasnopolsky V. A. (1993) Icarus 101, 313-332.


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